CALIFORNIA AGRICULTURAL EXTENSION SERVICE CIRCULAR 112 September, 1939 PRUNING DECIDUOUS FRUIT TREES WARREN P. TUFTS Cooperative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. B. H. Crocheron, Director, California Agricultural Extension Service. THE COLLEGE OF AGRICULTURE UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Terms used 3 Source of materials for tree and crop 5 Proper time for pruning 9 Pruning responses 9 Dormant pruning 9 Effect of summer-pruning young trees 12 Transition from nonbearing to bearing 14 Types of pruning 15 Heading-back and thinning-out 15 Bulk versus fine pruning 16 Spur pruning 16 Training the young tree: general principles 16 Training systems 20 Leader type 20 Delayed-open-center type 21 Open-center type 21 Pruning systems 22 "Short" versus "long" pruning 22 Winters system 25 Sims system 26 Caldwell system 26 Selection of a pruning system 28 Pruning bearing trees 31 Appearance of fruit buds 31 Recognition of fruit buds 33 New wood necessary for future f ruitfulness 34 Distribution of fruit wood 35 Fruit bud formation 36 Regular pruning 39 Regulation of size and quality of the fruit crop 41 Protection of pruning wounds 41 Correlation between pruning and other cultural practices 43 Practical suggestions on the shaping of young deciduous fruit trees 44 Training young almonds, apricots, nectarines, peaches, and Japanese plums 44 Training young apples, cherries, figs, pears, persimmons, European plums, prunes, and quinces 46 Training young pecans and walnuts 48 Practical suggestions for pruning bearing deciduous fruit trees 50 Almonds 50 Apples 51 Apricots 53 Sweet cherries 53 Figs 54 Peaches and nectarines 55 Pears 58 Persimmons 58 Japanese plums 60 European plums 62 Quinces 64 Walnuts 64 Summary of facts to be kept in mind when pruning young nonbearing trees. . . 65 Summary of facts to be kept in mind when pruning bearing trees 66 Acknowledgments 67 PRUNING DECIDUOUS FRUIT TREES WAEREN P. TUFTS 2 Pruning consists of cutting, removing, or repressing certain living parts of the tree in order to modify and utilize its natural habits for the grower's purposes. By pruning, the form of the tree is modified, its bear- ing is regulated, and more and better fruit is obtained at less cost and for a longer period than is otherwise possible. A tree so responds to any kind of pruning that one cannot modify its form without also profoundly influencing its functions. The various operations of pruning must there- fore be understood, as well as the mode of applying them, in order to obtain the necessary responses. Briefly stated, the chief purposes of pruning are : 1. To produce a vigorous, mechanically strong, healthy tree. 2. To secure a tree well shaped for convenience and economy in or- chard management. 3. To distribute the fruiting area well over the tree. 4. To secure fruit of good size and quality. 5. To regulate the annual succession of crops in order to obtain the maximum average crop compatible with good fruit. TERMS USED At the end of the first season's growth in the orchard or in the nursery, there will be in the axil (that is, the angle formed by the leafstalk and the one-year wood) of each leaf and on the end of the branches of such trees as the apple and pear, a mass of tissue known as a bud. In a tree one or two years old, all or nearly all the buds will consist of numerous scales that cover and protect a group of cells capable of actively divid- ing, growing, and producing a new shoot whenever the proper stimulus is provided and external growing conditions are favorable. Such a bud is a leaf or wood bud. Flower buds, or fruit buds (fig. 1), on the other hand, contain the ele- ments or unexpanded parts of a flower or flowers, with or without the rudiments of a leafy shoot. They may be divided into two groups : simple flower buds, which develop either into a single flower (peaches, apricots, x The material presented has been largely taken from Bulletin 313, Pruning Young Deciduous Fruit Trees, and from Bulletin 386, Pruning Bearing Deciduous Fruit Trees, both by the author of this publication. 2 Professor of Pomology and Pomologist in the Experiment Station. [3] 4 California Agricultural Extension Service [Cm. 112 almonds) or into several flowers (cherries, plums) ; and mixed flower buds, which develop into a cluster of leaves and flowers (apples, pears) . Buds may also be classified by their position on the shoot or tree, as Fig. 1. — Fruit bud of the peach. Note the two lateral fruit buds with a small leaf bud between. (From Bui. 386.) terminal buds, on the ends of the shoots ; and lateral buds, on the sides of the shoots. Dormant or latent buds are ones that are not forced into growth during the season immediately after their formation and that remain attached at the surface or buried in the tissues of the plant (fig. 2) . Practically all new growth arising from older branches and trunks of trees comes from these dormant buds rather than from adventitious buds, from which they must be clearly distinguished. Pruning Deciduous Fruit Trees 5 Adventitious buds are ones produced at unusual points (not leaf axils) on the roots, trunk, or branches. This kind of bud, which occurs frequently on the roots of such fruit plants as the myrobalan plum, gives rise to vigorous shoots called suckers. Similar vigorous shoots arising from trunks and older branches are commonly called water-sprouts, but these originate primarily from dormant buds. Fig. 2. — Dormant buds on old apricot branches are shown at A. These must not be confused with lenticels, B. Certain growths produced by lateral one-year buds and, to a much less extent, by dormant buds, are called spurs. These, produced by many species of fruit trees, are short shoots upon which are borne flowers and fruit. During the growing season, any new shoot is referred to as current, or this year's growth. In the following season, however, this same shoot- is called one-year wood. In a similar way, reference is made to two-year wood and the like. SOURCE OF MATERIALS FOR TREE AND CROP To comprehend the responses of the tree to pruning, one should know certain facts concerning its annual cycle of growth and development. The first growth of the season (blossoms, leaves, and new shoots) is made largely at the expense of plant-food reserves normally stored in the tree 6 California Agricultural Extension Service [ Cir - 112 during the preceding summer and fall. These stored foods are thus at least partially used up early in the spring. Carbohydrates, a most important class of foods for both plants and animals, are manufactured by plant leaves from carbon dioxide supplied by the air and from water supplied by the soil ; in this process, light and chlorophyll (the green coloring matter of leaves) are necessary. The complex materials needed for growth and development are elaborated from the minerals supplied by the soil and from the carbohydrates of the leaves. After the active vegetative period of early spring, the plant begins to store such elaborated foods as are not used in the maturing of the current fruit crop, the development of leaves, the extension of the top and roots, and the development of fruit buds for the succeeding year's crop. Under favorable conditions, the storage of reserves for the winter months and for the growth of the following year becomes greater and greater as the season advances, at least until near the time of leaf fall. A fruit tree with its crops represents an accumulation of materials drawn from the soil by the roots and from the air by the leaves. When the materials from either source can no longer be obtained, the tree ceases to live. Consequently, any plan for developing and managing an orchard from its planting to the time it is no longer profitable must in- clude the treatment of both soil and tree. Trees develop or produce differently in different locations and respond rather readily to cultural practices, especially pruning. One must consider, therefore, the relative abundance of the various foods or food materials. Changing the top by pruning is one way of changing the relative abundance of the foods. Top pruning necessarily reduces both the present and the potential growing points and leaf area, usually with the following effects : 1. A decreased food supply due to reduced manufacturing surface. 2. A greater percentage of reserve foods made available to the reduced number of growing points and fruits. 3. A decreased evaporation, resulting in a conservation of soil mois- ture and thus allowing a smaller tree to thrive over a longer period if water is limited. 4. A decreased root growth because of a reduction in the amount of energy-producing food manufactured. Much observational evidence and considerable direct experimentation show that plants respond differently in growth and in fruit production according to the amounts of nitrogen available, the amounts of carbohy- drates that can be manufactured, and the manner in which these are combined within the plant. Great differences likewise may be brought Pruning Deciduous Fruit Trees 7 about by variations in temperature and in the length of the light period to which plants are exposed. In fruit trees, the factors most likely to occur in limiting amounts are carbohydrates, nitrogen, and water. According to evidence gained from experience and experiments, four general classes may be set up to de- scribe the states of vegetativeness and fruitfulness in the plant. These classes present a good working concept of the response of the tree, al- though they do not necessarily indicate the cause. The four general classes or states are as follows : 1. Mineral nutrients (including nitrates) abundant, but no carbohy- drate supply available. Result: vegetativeness weak, and plant non- fruitful. 2. Mineral nutrients (including nitrates) abundant, and a carbohy- drate supply available. Result : vegetativeness strong, but little or no fruit. 3. Mineral nutrients abundant except nitrates, which are relatively less than in class 2. This condition reduces vegetativeness and causes carbohydrates to accumulate. Result : fruitfulness and a moderate amount of vegetative growth. 4. Mineral nutrients abundant except nitrates, which are relatively even less than in class 3. Result : a marked accumulation of carbohy- drates and a suppression of both vegetativeness and fruitfulness. Naturally these classes grade into each other, but one can place trees in one or another of them with considerable accuracy by observing the appearance and performance of the trees and by knowing the general cultural conditions employed. The crops produced and the new wood growth made generally furnish an excellent basis for judgment and a fairly accurate estimate as to what is happening in the plant. Heavy cutting, whether on young trees or old, generally results in rank vegetative growth and, with trees of bearing age, in reduction of fruitfulness. If, in addition to the pruning, the trees are irrigated and heavily fertilized, the new growth will be still ranker and more succu- lent, and little or no fruit will be produced (class 2). In bearing trees, on the other hand, a lack of pruning, of soil moisture, and of nitrogen will result in scanty new wood growth and in a tendency towards over- production. If this treatment is continued, trees soon reach a condition where little or no wood or fruit is produced (class 4) . Between these ex- tremes may be found all gradations of vegetativeness and fruitfulness. Fruit growers will readily recall orchards exhibiting varying degrees of vegetative vigor and fruitfulness. Unfortunately, many attempts in the past have been made to influence the wood growth and the produc- 8 California Agricultural Extension Service t ClR - 112 tiveness of the tree by pruning alone — an error, since pruning is only one of the factors modifying plant growth and productiveness. Irriga- tion, application of fertilizers, and cultivation (which kills the weeds that compete with the trees for water and nitrogen) are other factors to be considered along with pruning in any attempt to regulate the vege- tative growth and fruitfulness of an orchard. Trees just planted have relatively little carbohydrate, but enough to start them into growth. As they develop, leaves are formed, which manu- facture a new supply of carbohydrates ; and as the leaf area becomes greater, this supply is increased, the roots are extended farther into the soil, and the tree becomes vigorously vegetative — that is, it belongs to class 2. If, however, such young trees are severely pruned early in the summer, so that growth made from food stored the previous season is removed, and, in addition, the leaf area is seriously reduced, the tree will fail to grow as much as one less severely pruned or not pruned at all, other con- ditions being the same. This would tend to represent a class-1 condition. If, on the other hand, the young vigorous trees are less severely cut back, the consequent larger leaf area will permit a greater manufacture of carbohydrates. Then, provided the nitrogen supply is not markedly increased, there will be a tendency toward a decrease of vegetative activi- ties, with increase in carbohydrate accumulation ; and the trees will gradually become fruitful. Such plants fall in class 3. Since every com- mercial orchardist aims to maintain his trees in this class, he should select his methods of cultivation, irrigation, pruning, and the like with the idea of securing a proper balance between vegetative growth and fruitfulness. The production of a large number of fruits is not profitable unless it can be continued, and for this purpose a constant supply of new growth must be maintained as well. By knowing some of the materials concerned in the maintenance of this condition and some of the means for their regulation, the fruit grower has a direct and fairly accurate method of securing the type of tree he desires. The conditions of class 4 are commonly observed in old almond, prune, and pear orchards in California, which make little or no new growth : although there are many fruit spurs present, almost no fruit is pro- duced. In these cases, the difficulty is frequently a lack of nitrogen, since large quantities of carbohydrates have usually been stored in the top. Such trees as these, when nitrogen and moisture are supplied, or when nitrogen is already available in the soil and moisture alone is supplied, usually produce for a short period of years, but may fall back into class 4 unless the improved soil management is accompanied by adequate Pruning Deciduous Fruit Trees 9 pruning. Likewise, a pruning that removes much of the old wood and permits a relatively greater nitrogen supply to the remaining branches and buds greatly increases the vegetativeness of these portions and often the fruit production as well. To attempt to regulate such trees by prun- ing alone, however, would be futile, because balancing the top with the available nitrogen or moisture would mean reducing the top to a size that could hardly produce a commercial crop. One might far more profitably consider the soil requirements, as well as a more rational pruning method. PROPER TIME FOR PRUNING The old axioms, "Prune when the knife is sharp" and "Summer-prune for fruit and winter-prune for wood," are unsafe guides ; the fruit grower should have a more reasonable basis for timing his pruning practice. For all deciduous orchards in California, except in a few special cases (p. 12), pruning gives the best results when done during the dormant season — that is, after leaf fall and before new growth starts the follow- ing spring. PRUNING RESPONSES Dormant Pruning. — At the end of any growing season, the root and top development of a tree will tend to reach a balance : that is, the root sys- tem is extensive enough to supply the top with adequate moisture and mineral salts from the soil, and the aboveground parts are sufficient to manufacture the complicated foods necessary for the future develop- ment of the whole plant. When a young tree is dug from the nursery, with the consequent loss of roots, this balance is disturbed. If the top is not cut back at the time of planting in the orchard, too many buds will be left to grow, and the reduced root area will be unable to supply them with materials from the soil. This condition of unbalance may cause the tree to die or to make but a feeble start. If, however, the top is cut back at the time of planting, each remaining bud will have a larger propor- tionate share of the available moisture and of the mineral plant-food materials, and the subsequent growth will be more vigorous. One must remember that any pruning reduces, in proportion to its severity, not only stored food materials but also the potential leaf area, the principal "machinery" for manufacturing carbohydrates. Heavy dormant pruning undoubtedly restricts maximum root develop- ment. The roots, being incapable of carbohydrate synthesis, depend upon the leaves and the aboveground parts for their supply. If such supply is limited by top pruning, then the root system must be limited. A large 10 California Agricultural Extension Service t ClR - 112 top presupposes a large root system; and any limitation of root develop- ment tends, indireetly but surely, to restrict the growth of stems and branches. In growth, development, and fruiting, the water and mineral intake are quite as important factors as the substances built up or found in the tops themselves (figs. 3, 4, 5) . Fig. 3. — Five-year-old Nonpareil almond tree after pruning. This tree has been lightly pruned each year. Compare with figure 4 of an adjoining tree severely pruned annually, which was photographed at the same distance; note the relative sizes of trees and branches. Except for the pruning, these trees have received identical treatment. This is a representative specimen of a large number of trees similarly treated. (From Bui. 386.) These observations on the retarding effects of pruning apply especially to the young nonbearing tree, where the dwarfing effects of blossom- ing and fruit production need not be considered. As experiments have shown, the removal of blossoms in itself will produce an invigorating vegetative effect ; and, as every grower has noted, a heavy production of fruit is not accompanied by a luxuriant shoot growth. With these facts in mind, one can understand why the pruning of bearing trees may result in increased vigor, whereas the same severity of cutting may actually dwarf a young nonbearing tree : in the former case the invig- Pruning Deciduous Fruit Trees 11 Fig. 4. — Five-year-old Nonpareil almond tree after pruning — a representa- tive specimen of a large number of trees similarly treated. This tree has been heavily pruned each year. Compare with figure 3. (From Bui. 386.) Fig. 5. — Trunks and main roots of five-year-old Nonpareil almond trees, from the planting described in figures 3 and 4 ; tree A was lightly pruned each year ; tree B, heavily pruned. Note the greater trunk and root development of tree A. 12 California Agricultural Extension Service [ Cir - 112 orating effect of removing part of a potential fruit crop more than com- pensates for the dwarfing effect of losing some of the potential leaf area. Effect of Summer-Pruning Young Trees. — The abundant literature on the various phases of pruning contains many references to "summer pruning." In nearly all instances, this practice has been intended to increase the fruitfulness of full-bearing trees, but this is of little impor- tance in California. Summer cutting in training the young nonbearing tree must be considered, however, both because of its importance and because of its widespread use during recent years. If the tree makes an excellent start, pruning may profitably begin the first summer after planting. As soon as the young tender shoots are 3 or 4 inches long, the trees should be carefully examined, and any growths not to be utilized in building the main framework of the tree pinched back. If the work is done at this time, all the strength of the plant will go toward a heavy vigorous growth in the remaining branches, which are to be permanent. Very often the suppression of shoots undesirably placed, by merely pinching off the tips, will induce growth where wanted. It is wise to go over the orchard about a month or six weeks after this first thinning to see that no new, vigorous, undesirable shoots have arisen. In suppressing the undesirably placed growths, one should spare two or three leaves next to the trunk to shade it and thus prevent sunburn. The question is sometimes raised as to the advisability of heading back the three main branches the first summer : the best results have been secured by allowing them to grow undisturbed unless length growth is very rapid and the total growth is 5 feet or more ; in these cases, the weight of the leaves may break the branches, and the branches should be headed at the height desired for secondary branching. During the second and succeeding summers and until exuberant wood growth is slowed down by fruiting, the vigorously growing trees often need a pruning early in the season in order to direct all their energies into the branches that will be retained as the future framework. If the trees are favorably located and make a vigorous start the second summer, the new shoots usually attain by the middle of May a length equaling or exceeding that which should be left at the second dormant pruning. With the long growing seasons experienced in nearly all the deciduous-fruit sections of California, the dormant pruning usually performed the sec- ond winter may be moved up to the preceding May with the object of obtaining the ordinary second and third seasons' shaping during the second season. Pruning done at this time not only hastens the training of the tree but removes many unnecessary shoots and thus reduces to the minimum the second dormant pruning. Pruning Deciduous Fruit Trees 13 One must exercise judgment in adopting this system of summer prun- ing : trees must be grown under favorable soil and moisture conditions. If the pruning is done early in the season and if other conditions are as outlined, an orchard under such treatment should come into profit- able bearing sooner than otherwise. Whether this early-summer training should be continued during the third and fourth summers depends upon the exuberance of growth and upon the formation of fruit wood. If the trees show no indication of settling down to fruiting and if the vegetative growth is so dense that fruit spurs on the lower portions of the tree are shaded, then summer pruning, especially a thinning process, may be advisable in later years. Likewise, if sufficient branching has not been obtained, this early-summer pruning may be employed for several sea- sons, being of special value in securing spread with obstinate upright- growing trees like the sweet cherry. Summer pruning at any time is devitalizing, and midsummer cutting is more weakening than cutting done early in the season. Early-spring growth is made at the expense of stored food material. To remove part of the foliage before these new leaves have had an opportunity in turn to manufacture and store plant food, robs the plant. After active shoot elongation ceases, the plant turns its energies to manufacturing and storing plant food for the succeeding year. The later a pruning is given in the growing period during which active shoot elongation is taking place with no corresponding storage of plant food, the greater will be the loss to the plant, provided such pruning is proportionately heavy. If the cutting during the latter part of the summer is designed to give the same relative shape as results from a pruning early in the season, more wood must be removed by both thinning and heading, especially if the new branches are to be secured at approximately the same height from the ground. Under the arid conditions in many orchard sections of Califor- nia, the soil moisture may be insufficient to force a vigorous new wood growth late in the season even if such growth could be properly matured before the frosts of early winter. The orchardist practicing late-summer pruning on young trees will lose in a twofold manner : 1. The leaf area of his trees will be reduced right at the beginning of maximum storage of plant food in fruiting and vegetative parts. 2. Since no benefits may accrue from late-summer pruning, he will lose the cost of the pruning. Despite the reduction in vigor just noted, results from practical appli- cations of an early-summer pruning seem to justify the practice, pro- vided the trees are growing thriftily and provided the work is done as 14 California Agricultural Extension Service t ClR - 112 early as possible in the growing season — in most locations not later than the first week in June and preferably by the middle of May. Transition from Nonbearing to Bearing. — The lighter the pruning of young trees, consistent with the securing of a proper framework of scaffold branches, the greater will be their development, and the sooner will profitable crops be produced. The more severely young trees are & n Fig. 6. — What is meant by the expressions thinning out and heading back: A, an apple branch with one-year shoots thinned out 50 per cent ; B, an apple branch with one-year shoots headed back 50 per cent; C, an apple branch with one-year shoots thinned out two-thirds; D, an apple branch with one-year shoots headed back two- thirds. (From Bui. 313.) pruned, the longer they remain unfruitful. Continued heavy cutting not only lessens the chances for a fruit crop, especially with spur pro- ducers, but materially reduces wood development (figs. 3 and 4). According to common experience with fruit trees just beginning good production, injudicious heavy cutting during one season may so dis- turb the delicate balance between wood growth and fruiting as to delay profitable cropping for three or four years. One must exercise the best judgment in selecting the pruning treatment for a particular orchard, especially when the trees are just approaching the bearing age. As the trees become older and bearing is fully established, heavier Pruning Deciduous Fruit Trees 15 pruning may often be necessary in order to continue regular bearing while maintaining the necessary wood growth. To this end, supplemen- tary fertilization may be advisable or even necessary. TYPES OF PRUNING Heading Back and Thinning Out. — Any pruning that leaves a stub, no matter how old the wood, may be considered heading. In thinning out, v •/- -J-y' < fjT s \ I 1/ ,#' f \ ■r"'^ dm U i 1/ /' 1 • "V ii p3 &^a| ■ \ #3 1 I -^vj ill P IX 1 J*yl iMF^* ^>^**^ • /^ l^^^x /• A J **rf^*® a ^ i *fI\ ' Jpr\ Mm * y j£~~* I H" ~Jm ! ■iff-V > -' ■* l||F v^JBr ; : J? - Jjr ^»^^^^py # ,. Fig. 7. — Pruning by thinning out. The A's indicate typical cuts. a branch is either removed entirely or cut back to a lateral. If the new wood of a tree is given a 50 per cent heading -back, the terminal half of the past season's growth has been removed (fig. 6, B) . A 50 per cent thin- ning-out means that half the number of one-year shoots have been re- moved entirely, the remaining half in no way being cut (fig. 6, A) . These terms are not necessarily confined to the cutting of one-year wood (fig. 7) . 16 California Agricultural Extension Service [ Cir - 112 Bulk versus Fine Pruning. — The question may well be asked whether or not pruning should consist in a few large or in many small cuts well distributed over the tree. Horticulturists generally consider that the im- mediate influence of a pruning cut does not extend far from the place it is made and that the pruning should therefore be distributed over as large a portion of the tree as is economically possible. (Of course the total amount of cutting does eventually influence the tree as a whole.) Whether the cuts should average %, y 2 , or 1 inch in diameter largely depends upon the species. With the peach, where the bulk of the fruit wood must be renewed annually, many cuts are necessary to secure a large number of new shoots well distributed. With species producing on spurs, how- ever, comparatively few cuts may often suffice. Bulk pruning, by removing relatively large limbs, commonly gives rise to numerous water-sprouts. These may at times be utilized in rebuilding the framework of the tree ; and a few, under favorable conditions, may be converted into part of the fruit-spur system. Generally, however, water-sprouts are of little value and should be removed entirely as soon as they appear. Spur Pruning. — Spur pruning is essentially "fine" pruning. It is often utilized in rejuvenating orchards which, for one reason or another, have fallen into class 4 (p. 7). It consists in removing whole spurs or portions of spurs, and it tends to stimulate vegetative growth. Because of the labor cost involved and the fact that most trees are very brushy, comparable results are usually secured by a somewhat "coarser" method of cutting. TRAINING THE YOUNG TREE : GENERAL PRINCIPLES Fruit trees do not increase in height except through the growth of buds and the elongation of the terminal growing point. The height of the main trunk is determined when the tree is cut back at time of planting. In this discussion, the term height of head will refer to the distance be- tween the ground and the lowest scaffold limb. The lower the head, the greater the shading of the trunk and the less the sunburn, or sunscald. This point should be especially emphasized for orchards in the hot in- terior valleys. Sufficient trunk space should be left so that at least 6, preferably 8 to 12, inches will intervene between the primary scaffold limbs. Thus if the young tree is arbitrarily cut off at 24 inches from the ground and three primary scaffolds are selected, the lowest one should stand 8 to 12 inches from the ground. Personal preference will determine the number of primary scaffolds, but care should be taken not to have too many ; two or three at the first dormant pruning will prove sufficient. Pruning Deciduous Fruit Trees 17 Four or five primary scaffolds necessitate cutting the tree rather high at planting time or else spending several years in developing them. At 5 feet from the ground, five to seven primary and secondary scaffolds are all that can usually be accommodated without crowding. At all times, the grower should have in mind his ideal tree as it will appear at maturity and should prune accordingly. If three primary scaffolds are selected, they should be properly bal- anced around the trunk, forming equal angles of about 120 degrees each (fig. 8) ; but — more important — they should be spaced up and down Fig. 8. — Looking downward on a young tree, showing a satisfactory arrangement of primary scaffold branches around the trunk. This will give balance and symmetry to the tree. (From Bui. 313.) the trunk as directed above (figs. 9 and 10). These primary scaffolds should be headed at 15 to 30 inches or more from their juncture with the trunk. The severity of this first heading depends upon the total length of new wood, its angle of growth, and the formation of lateral branches on current season's wood (as in the case of the peach). Al- though general statements may be somewhat misleading, it is necessary here to give some idea regarding the amount of heading-back the young tree should receive at the first dormant pruning. The greater the amount of one-year growth, the longer the branch may be left ; the secondary branching, however, must not come too high. The more horizontal the growth, the more severe will be the necessary head- ing-back in order to secure the uprightness necessary for mechanical strength and ease of cultivation. Trees forming branches on current season's growth may be headed more lightly or not at all ; such heading, as is given, since it comes above the forks formed naturally during the 18 California Agricultural Extension Service [ Cir - 112 growing season, is designed not to secure additional branching, but rather to secure proper angle and spread. The primary scaffolds, headed lightly (as above indicated) at the end Fig. 9. — Apricot tree after one season's growth in the orchard. (From Ext. Cir. 51.) of the first growing season, will allow sufficient room for the secondary scaffold branches to develop the second summer. With such fruits as the almond, apricot, peach, and Japanese plum, no further heading is desir- Pruning Deciduous Fruit Trees 19 able (if sufficient branching and spread have been obtained with the one light heading) until the tree comes into full bearing, at which time active vegetative growth is naturally retarded. Under certain conditions, cher- ries, pears, and other fruit trees with similar growth habits require one or more additional headings (either winter or summer) to form the nec- essary framework and to secure the desired spread. Varietal character- istics and climatic environment largely determine whether or not lateral branches will be formed by using only a thinning-out system of pruning. The Bartlett pear, for ex- ample, under certain conditions throws laterals without being headed back, but under other conditions must be headed to force laterals. As already pointed out, heavy pruning will subdue and light prun- ing will encourage total growth in young trees. This rule applies read- ily to the maintenance of the proper balance between various parts of the young tree. To encourage any branch or portion of a tree, there- fore, one must prune it rather lightly in comparison with the branches or parts with which it must compete. In this connection, attention must be called to the bad results of even cutting (fig. 12). If two shoots fork- Fig. 10. — The same tree as in figure 9, after pruning. Spacing of primary scaffolds up and down the trunk must be sufficient to secure mechanical strength and to avoid weak, debris-catching crotches. Compare with figures 11 and 19. (From Ext. Cir. 51.) ing from the same branch are headed evenly, they tend to develop equal- ly, with a resultant sharp-angled crotch, which is usually mechanically weak. If, on the other hand, the shoot that best continues the general direction of the framework of the tree is cut longer, it will grow strong. The second shoot will, in conse- quence of being cut shorter, develop into a minor branch with a strong, broad-angled crotch (fig. 13) . Three branches should never be allowed to 20 California Agricultural Extension Service [Cir. 112 arise from one point, either in formation of primary framework or at any time in the pruning of the tree (figs. 11 and 14) . TRAINING SYSTEMS There are three systems of training fruit trees : 1. The leader or pyramid type. 2. The delayed-open-center or modified-leader type. 3. The open-center or vase-shaped type. Fig. 11. — Two-year-old apricot tree broken down because of weak crotch. Scaffolds emerged too close to each other on the trunk. Compare with figures 16 and 17 of a two-year-old tree with well-selected scaffolds. Leader Type. — The leader type of tree, once fairly common in Amer- ica, is still found in some of the older orchard sections of the East, as well as in Europe. The topmost branch is encouraged to gain the ascendency (fig. 15) ; and as time passes, the tree becomes pyramid-shaped, although, because of shading by the upper branches, it is sometimes difficult to maintain the lower ones. This type of tree, however, has nothing to rec- Pruning Deciduous Fruit Trees 21 ommend it to the commercial orchardists of California, with the possible exception of the walnut growers. Delay ed-0 pen-Center Type. — Trees of the delayed-open-center type are occasionally seen in California, although not to the extent the system merits. At the first heading-back, the top- most limb is left considerably longer than the others (fig. 10) . The result is the strong growth of this limb (figs. 16 and 17). At subsequent prunings, growth from this top- most limb must be subdued by heavy cut- ting, and the remainder of the tree allowed to thrive (fig. 18). The reason for uneven cutting at first, followed by a repression of the favored part, is to permit a greater spacing of the scaffold limbs on the trunk (p. 16) . Many varieties of the apple, cherry, pear, apricot, and European plum (includ- ing the prune) adapt themselves particu- larly well to this style. The term "delayed open-center" is used advisedly because, by the system just outlined, the tree is opened out like the true open-center tree, with the difference that in the latter type of pruning the open center is obtained immediately at the time of the first heading-back, whereas in the former case two or three or four years may be necessary. Trees pruned by the two methods may be expected to come into bearing at about the same time, though with the delayed-open-center tree some- what stronger and better formed than the strictly vase-shaped tree. Open-Center Type. — Probably 75 per cent or more of the deciduous fruit trees in California are of this general type. Properly applied, the system has proved entirely satisfactory. The one glaring defect has been the encouragement of all scaffold limbs to arise from one point on the trunk, with the formation of basin crotches or "water pockets" (fig. 19) , especially in upright-growing varieties such as the French prune. Con- sequently heart-rot occurs, with breakage from a heavy load of fruit when the trees should be producing maximum crops. Under this system, Fig. 12. — Equal develop- ment of branches and resulting sharp-angled, weak crotch (at A) occasioned by even cutting at B. (From Bui. 313.) 22 California Agricultural Extension Service [Cir. 112 branches arising from the main trunk are given equal encouragement from the first. Care must be taken, however, to leave the topmost branch several inches longer (figs. 20 and 21) . Otherwise, the upper branch will often be choked out by the more rapid development of the two lower branches (fig. 22). The centers are kept as open as is compatible with Fig. 13. — Unequal development of branches and mechanically strong crotch caused by uneven pruning at points A and B. These branches are of the same age, but are unequally developed because of uneven cutting. (From Bui. 313.) freedom from sunburn of the branches. The degree of openness of the center varies with the species, with local conditions, and with the grow- er's personal ideal. PRUNING SYSTEMS "Short" versus "Long" Pruning. — There has been much discussion in California regarding the relative merits of the so-called "long" and "short" pruning of deciduous fruit trees. It is rather difficult to draw a definite line between these two systems because with their modifica- tions, they merge into each other. Briefly, the system of "short" pruning consists essentially in a rather Pruning Deciduous Fruit Trees 23 severe thinning-out, accompanied by a heavy heading of the new growth, whereas "long" pruning consists essentially in a moderate thinning-out and in keeping the tree within bounds by cutting to laterals that are left untouched. Although the latter system removes somewhat less wood, the Fig. 14. — Portion of the framework of a young bearing apricot tree. Note the crowded condition of the scaffold branches caused by allowing three branches to arise at one point, A. Difficulty would have been avoided if the cuts indi- cated at A and B had been made three or four years ago. conclusion of many growers that it really amounts to little or no pruning is incorrect. Throughout the state, during the past twenty years, there has been such a tendency towards less severe pruning that now one cannot easily distinguish between orchards "short"- and "long"-pruned. Thoughtful and observant orchardists realize that the same principles of plant 24 California Agricultural Extension Service [Cir. 112 growth and response apply with equal force to all systems of pruning. As their idea of the relation between vegetative growth, tonnage, quality, and economy of orchard management becomes clearer, they recognize that the different systems now in use merge into each other and that the Fig. 15. — The central-leader type of walnut tree. This type has a strong framework of branches and plenty of fruit wood. (From Bui. 379.) best system for any particular case will lie at some point between the extremes of "short" and "long" pruning. Several modifications of the "short" and "long" systems are in vogue in certain sections of California. Undoubtedly many growers who are fol- lowing one of these methods may differ as to the classification here made. Figures 23 and 24 show an example of a type of "short" pruning for- merly much used with deciduous fruit trees in California. This method, Pruning Deciduous Fruit Trees 25 not now so generally applied, consists essentially in a heavy thinning, with the removal of all but three or four buds on the shoots that are headed. Certain growers have worked out for their own conditions satisfactory 1 \\M il i/i I "n. y Ufm / A : - Nffi ■■JnfffijFri fe|P| ^M ■ f /■ \ \# 1/ £ Jm mI \j \"'K \>0m / wM "wmM^ 1 ^ llfcf yf N \ x ^ Wv?#/fr 3 r ~mvm\ &y ~~\ % \jfeJr / Fig. 16. — Two-year-old apricot tree before pruning. Com- pare with figure 17, after pruning. At the end of the first year, this tree was much the same as the tree shown in fig- ures 9 and 10. systems of training and pruning that are distinct departures from the ordinary methods. Winters System. — Figure 25 shows an apricot tree trained by the so- called "Winters system." This flattened expanse of the fruiting area is designed to give better exposure to the sun with the object of ripening the fruit earlier. It does not, however, bring about the result desired, because the heavy cutting gives rise to succulent vegetative growth early in the season, the shade from which more than offsets the advantage of a flat top. This method of training is also objectionable because the upper sides of the main branches are often badly sunburned. The result 2(5 California Agricultural Extension Service t ClR - 112 is wood decay, even though the vegetative growth during the following spring is sufficient to shade the fruit and retard its development. More- over, restricting the height of the tree so that all work is clone from an 8-foot ladder materially reduces the fruiting area and the possible ton- age of fruit of high quality. Fig. 17. — Two-year-old apricot tree after priming. Com- pare with figure 16, before priming. Note the dominance of the central branch, which will be gradually subdued, and the five secondary scaffold branches. This type of training will eventually result in such a tree as shown in figure 18. Sims System. — Figure 26 shows a mature peach tree pruned by the "Sims system," of which the relatively few upright scaffold branches clothed with long, slender fruiting twigs are characteristic. These scaf- folds can hold a heavy load of fruit with the minimum of bracing. The rather narrow spread of trees thus pruned is perhaps an unwarranted restriction of the fruiting area : trees pruned by this system do not yield maximum crops. Caldwell System. — One interesting departure from standard pruning Pruning Deciduous Fruit Trees 27 practice is the so-called "Caldwell system" for pears (fig. 27). Briefly stated, this consists in tying; down the upright one-year shoots at an angle somewhat below the horizontal. The resultant new growth arises just below and behind the highest point of the bend. Practically all growth beyond this point is reproductive in character and rapidly de- velops a good fruit-spur system. In principle, the Caldwell plan closely Fig. 18. — Twelve-year-old apricot tree after pruning. Note the strong scaf- fold framework with excellent vertical distribution. This tree was started by the modified-leader system as shown in figures 9, 10, 16, and 17. resembles the espalier method of training used in Europe. In both cases, the bending of the branches seems to induce fruitfulness. At each dor- mant season, all the new shoots are so tied down that there is little shad- ing of the lower branches. The later tying is done to any convenient point on either trunk or branch. Briefly, the advantages claimed are that large trees of good mechanical strength, combined with a large fruiting area close to the ground, are secured in a comparatively short period; that they come into bearing two to four years earlier than trees trained by severe cutting back ; that they can be trained to a more shapely form in a windy section or where prevailing winds hinder symmetrical development; and, finally, that they produce larger crops of satisfactory quality. The chief disadvantage is that this system, to be successful, must be part of a comprehensive and intensive orchard program. Since more 28 California Agricultural Extension Service [ Cir - 112 wood is conserved than with other methods, the grower mnst provide adequate moisture and fertility in order to secure an abundance of new wood while carrying large crops through to maturity and while supply- ing the enormous leaf area, which is being increased from year to year. In most soils, as soon as the trees begin bearing heavily, some renewal Fig. 19. — The result of selecting branches arising from one point on a main trunk. This photograph is of a ten-year-old almond tree. The trouble is just beginning. (From Bui. 313.) pruning is necessary in order to replace the fruit wood that has outlived its usefulness and to maintain a proper condition of vegetative vigor. Success largely depends upon skill and judgment. The method is prob- ably applicable only to pears during the years of training and should not be adopted without a full understanding of its requirements and limi- tations. Selection of a Pruning System. — The first and most important ques- tion to be asked is, will the system chosen insure the annual production of a good tonnage of high-quality fruit ? The growth of new wood is prob- ably the only index by which the grower can judge whether or not future Fig. 20. — One-year-old peach tree before and after pruning. (From Ext. Cir. 98.) Fig. 21. — Two-year-old peach tree before and after pruning. (From Ext. Cir. 98.) 30 California Agricultural Extension Service [ Cir - 112 - IBlIt w% ■ W .;, > ■ JH >-*;, HHK* -<., / *^HL . wmpp' ^^Hhk*** •"TaHKr '.* /JSP - j 1 jPp /mm ™i\J[ 1/ ■ "JH^B ; - &C i J ^HhK, , ^P sa^"* n^'< ^mfa* \ V B ffil wHH^BSHlik ' Hi * — "H B \. fmm fl H ^R ; ' ^ || , \ BR ?*"' , j. \ f/c^v-.; a- 7* /v \j^Mj^ \ 1 ^ t^Wwliiii^wiiB&^^ • '■'.- \ %'-%$'* K / i-Mfc ^Mfc— •:^> -x - « ' i - ' * * > ' ~ <•' 4 - - " % Fig. 22. — Note the choking-out of the central or topmost branch by the more vigorous growth of the lower branches. (From Ext. Cir. 98.) Pruning Deciduous Fruit Trees 31 yields are being sacrificed for the sake of one or two heavy crops. On the other hand, the production of too much vegetative growth will reduce the yields far below the maximum that can be profitably maintained. PRUNING BEARING TREES To prune fruit trees intelligently one must thoroughly understand the fruiting habits of the various species and must be able to distinguish between fruit and leaf buds. Fig. 23. — Mature Boyal apricot tree pruned by the so-called "short" system, which consists essentially in a severe thinning-out and heading-back of new wood growth. Note the lack of fruit spurs in lower parts of tree because of shad- ing out. Too many main scaffold branches. (From Bui. 386.) Appearance of Fruit Buds. — The fruit buds of the apple, pear, peach, apricot, and plum are larger and plumper than the leaf buds, and less sharply pointed. Cherry fruit buds are difficult to distinguish until they begin to swell. The most certain way of determining fruit buds is to section them lengthwise with a sharp knife or razor. The fruit buds of the apple, pear, cherry, and plum contain several roundish bodies, each of which develops into a flower. The fruit buds of the almond, peach, 32 California Agricultural Extension Service [Cir. 112 Fig. 24. — Fifteen-year-old Bartlett pear tree typically "short"-pruned. Note the severe thinning and heading-back. Only three or four buds have been left on each one-year shoot. (From Bui. 386.) Pruning Deciduous Fruit Trees 33 and apricot each contain the rudiments of a single flower. A pocket mag- nifying glass is helpful in this examination. Recognition of Fruit Buds. — A knowledge of the usual position of fruit buds is helpful, especially during the dormant season, in deter- TABLE 1 Position of Fruit Buds of Deciduous Fruits Fruit Almond Apple Apricot Cherry, sour. . . . Cherry, sweet. . . Fig Nectarine Peach Pear Pecan Persimmon Plum, European Plum, Japanese. Quince Walnut Lateral on long shoots Minor crop Minor crop Minor crop Major or minor crop Minor crop Major crop Major crop Major crop Minor crop Minor crop, young trees Major crop Minor (very few) Minor crop Major crop Minor crop, young trees Terminal on long shoots Few Few Major crop, young trees Minor crop Minor crop Major crop, young trees Lateral on spurs Major crop Major crop Minor or major crop Major crop Minor crop Minor crop Minor crop, mature trees Major crop Major crop Minor crop, mature trees Terminal on spurs Major crop Major crop Major crop, mature trees Major crop, mature trees mining the prospects for a crop the next season. The following key and table 1 give this information for the more important deciduous fruits. 1. On comparatively long shoots of the past-season one-year wood : a) Lateral (fig. 1, p. 4) : In this position are found almost all the fruit buds of the peach, quince, and olive ; part of those of apricots, almonds, plums, and cherries, and sometimes of pears, apples, and wal- nuts ; and the fruit buds for the first crop of figs. Apricots, peaches, and Japanese plums often bear three buds at a node, in which case the center one is usually a leaf bud and the two outer ones are fruit buds. b) Terminal : This is the normal position of most of the fruit buds of 34 California Agricultural Extension Service [ Cir - 112 the walnut. Some varieties of apples and pears also frequently bear a considerable number of fruit buds in this way. 2. On comparatively short shoots (spurs) of the past season. (These short shoots constitute either an extension of the spur sj^stem already established or the beginning of a new spur.) Fig. 25. — Winters system of apricot pruning. Note the low-spreading top and the severity with which new shoot growth has been headed. (From Bui. 386.) a) On short- or medium-lived spurs, which may live one to eight years (figs. 28 and 29) . Most of the fruit buds of apricots, plums, and almonds are borne laterally in this position. Peaches occasionally bear a small part of their fruit buds in this manner. Listed in the order of the usual length of life of the fruit spurs, from the shorter to the longer span, are the peach, the apricot, the almond, and the plum. b ) On long-lived spurs which live ten to twenty years but which should be renewed (or at least invigorated) oftener. Most fruit buds of sweet cherries and part of those of sour cherries are borne laterally, and most of the fruit buds of the apple and pear (fig. 30) terminally on such spurs. New Wood Necessary for Future Fruitfulness. — As previously sug- gested, the amount and character of the new wood produced during any season may serve as an index to the conditions existing within the tree. The amount of new vegetation necessary to maintain the correct balance apparently differs with the species in question. In general, in fruits like the peach, which bear most of their crop on one-year wood, fruitfulness is associated with a relatively greater amount of new growth than seems Pruning Deciduous Fruit Trees 35 necessary with spur producers. In spur producers, the species with the longest-lived spurs apparently need the least amount of new wood. This seems reasonable, since at least part of such new growth must be used Fig. 26. — Mature peach tree pruned by the Sims system. Note heavy framework branches. Fruit is produced on long pendent "hangers." By this unusual method much fruit is produced on spurs. After reaching a certain height (12 to 16 feet), trees are never allowed to grow taller. (From Bui. 386.) for replacing fruit wood that has outlived its usefulness. The amount of new growth necessary for continued fruit fulness may vary from a few inches, in such fruits as the apple and pear, to from 2 to 4 feet in the peach (table 2). Distribution of Fruit Wood. — Pruning is of value in distributing fruit wood uniformly throughout the tree and thus securing greater ton- 36 California Agricultural Extension Service [Cir. 112 nage of better quality. By this means, the trees are kept within bounds and the costs of maintenance and harvesting are reduced. TABLE 2 Desirable Amounts of New Growth for Bearing Trees Fruits Under 10 years of age Over 10 years of age Peaches 20 to 40 inches 12 to 30 inches 10 to 24 inches 9 to 18 inches 12 to 30 inches Apricots 10 to 24 inches Plums (except prunes) and quinces 9 to 18 inches 6 to 10 inches Fruit-Bud Formation. — Sufficient light in all fruit-producing parts of the tree is essential for uniform distribution of fruit buds. Pruning is pip Fig. 27. — Caldwell system of pear pruning. Six-year-old Bartlett pear tree trained by tying down new shoots each year. Note new branches arising at the bend. These will in turn be tied down to a position a little below the horizontal. (From Bui. 386.) practically the only means of securing favorable light distribution (see p. 41) . In general, a thinning-out is more conducive to fruit-spur forma- tion than a heading-back method of pruning (fig. 31) . Although fruit buds for any crop begin their visible development the previous summer (June to August, under practically all California con- Pruning Deciduous Fruit Trees 37 — y~ - sm ^ > £ Fig. 28. — Apricot fruit spurs: A, two years old; B, one year old. Scars where fruits have been produced are shown at x; fruit buds at y ; leaf buds at 2. (From Bui. 386.) 38 California Agricultural Extension Service [Cir. 112 Fig. 29. — Fruit spurs of plums; left to right: Eobe de Sergeant (European) ; Wickson (Japanese) ; Yellow Egg (European). Note small roundish fruit buds of the Wickson, characteristic of Japanese plums. The Robe de Sergeant has a more compact spur system than most European plums. (From Bui. 386.) Pruning Deciduous Fruit Trees 39 ditions), the pruning of bearing trees at that time is nevertheless of doubtful value as a means of securing greater f ruitf ulness. Regular Pruning. — Optimum results are obtained only when the prun- ing treatment is consistently and regularly carried out over a period of r-A Fig. 30. — Three-year-old portion of a pear spur. Note terminal fruit bud at A, two lateral leaf buds at B and B. Fruit was produced at C during the season preceding that in which buds A and B were formed. Growth of B buds will give rise to characteristic branching of older pear spurs. (From Bui. 386.) years. With some species, the trees may be left unpruned for several years ; but the net returns over a period of years will be smaller than those secured from annual cutting, which insures a constant renewal of fruit wood. Pruning should be part of each season's operations, even though the amount of wood removed may in some instances be com- paratively small. 40 California Agricultural Extension Service [Cm. 112 Fig. 31. — B, A two-year-old prune branch not headed back at the end of the pre- vious season ; note the production of fruit spurs, together with a sufficient amount of new wood. A, A two-year-old prune branch which received a heading-back at the end of the previous season; note the production of shoots and the lack of fruit spurs. (From Bui. 313.) Pruning Deciduous Fruit Trees 41 Regulation of Size and Quality of the Fruit Crop. — Since fruit trees normally tend to produce more fruit than can be successfully carried through to maturity, it is established orchard practice to reduce this burden somewhat at the annual dormant pruning. Because of certain fruiting habits, danger from spring frosts, liability to the June drop, and other factors that may decrease the final crop, not all the thinning of fruit can be done with the pruning shears. If pruning is used to reduce the number of fruits set to a point where hand-thinning can be definitely eliminated, the crop produced must be limited to less than that which the trees can successfully mature. Such severe pruning as this is, more- over, detrimental to future productivity. There is apparently a direct correlation between new vegetative growth and size of fruit. Trees that make a satisfactory wood growth usually bring the fruit crop through with larger sizes than trees that are unsatisfactory in this respect. Color, size, finish, and flavor constitute quality in fruits. With certain fruits, light is of prime importance in securing color, but if the tree is rightly "opened up" by pruning, little difficulty will be experienced in this connection. In allowing light to penetrate to the interior of the tree, one must not expose the scaffold branches to the sun's direct rays, for the result would be sunburn, with subsequent decay of the wood. Likewise, the new growth must be sufficient to shade the fruit and protect it from sunburn, especially in the dry, hot interior valleys. PROTECTION OF PRUNING WOUNDS If a tree is properly pruned from the start, the removal of large limbs can usually be avoided. In the removal of large branches, all cuts should be made close to the limb from which the branch arises (fig. 32), so that no stub is left (fig. 33). This method will greatly facilitate the healing of the wounds. The treatment of pruning wounds depends largely upon local condi- tions. In a section like the Watsonville apple district, where the foggy climate favors the germination and growth of the fungi that cause wood decay, the pruning cuts should be disinfected as soon as the wood has dried a little, but before any cracks have formed. Bordeaux paste is a good disinfectant and wound covering but must be replaced every year or two until the wound has completely healed. Where the air is relatively dry, pruning wounds seldom need disin- fection. But, in any case, large wounds should be covered with some protective substance — not to aid the healing, but to prevent the entrance 42 California Agricultural Extension Service t ClR - 112 of rot-causing fungi. All wounds 1% inches or more in diameter should be covered. Besides bordeaux paste, other materials that are not disinfectants are Fig. 32. — A well-made pruning cut. Note the callus formation, which in the course of a few years will completely cover the large wound. Compare the size of the cut with the quarter-dollar. (From Bui. 386.) often used for wound coverings. White lead paint mixed with raw linseed oil has been widely used. There are on the market many proprietary materials, most of which are asphaltum compounds or emulsions, to be applied cold. Pruning Deciduous Fruit Trees 43 CORRELATION BETWEEN PRUNING AND OTHER CULTURAL PRACTICES Although pruning* alone will not regulate the growth and. productivity of the orchard, it is doubtless among the most important factors in de- termining the balance between carbohydrate and nitrogen supply. The Fig. 33.— Improperly made pruning cuts. Such stubs will never heal over and are a constant menace as affording an entrance to Avood-rotting organisms. (From Bui. 386.) grower must thoroughly understand the principles involved before adopting a pruning system for any particular set of conditions. There may be an adequate supply of available nitrogen ; but if soil moisture is so greatly reduced that the tree cannot utilize this food mate- rial, then the pruning must maintain a proper balance. Pruning under such circumstances should probably be somewhat heavier in order to reduce the amount of water lost through evaporation. It should also keep the proportion of nitrogen to the carbohydrates present or being manufactured the same as if sufficient soil moisture and nitrogen were available. In the same way, fertilizers, irrigation, and cultivation affect the prun- 44 California Agricultural Extension Service [ Cir - 112 ing practice by limiting or increasing the amounts of soil moisture and available minerals, especially nitrogenous compounds. PRACTICAL SUGGESTIONS ON THE SHAPING OF YOUNG DECIDUOUS FRUIT TREES For the purpose of this discussion, the different deciduous fruits may be roughly grouped into two classes according to habit of growth. The first class contains those fruit trees that form side branches on current sea- son's growth (fig. 20, p. 29) ; this includes the almond, apricot, nectarine, peach, and Japanese plum. The trees of the second class (fig. 31, A) — the apple, cherry, fig, pear, pecan, persimmon, European plum, quince, and walnut — do not usually form side branches on the current year's wood. Different pruning may, however, be needed for trees in the same class. In general, the trees of the first class can be brought into bearing some- what sooner than those of the second. Likewise, a symmetrical framework is more quickly and easily formed by the trees in the first class. Training Young Almonds, Apricots, Nectarines, Peaches, and Japa- nese Plums. — 1. At planting, the nursery tree should be cut at a height of 24 to 30 inches above the ground. With the fruits of this class, the head of some of the trees may be shaped at planting time by utilizing side branches formed in the nursery. In case these branches are unsuitable, they should be cut back to a half -inch stub or a single bud. In this operation, care should be taken not to injure the ring of tissue surrounding the twig at its juncture with the trunk : it is from this tissue that new shoots arise. 2. The young tree should receive a coat of whitewash soon after plant- ing, to prevent sunburn on the trunk. 3. During April, the tree should be carefully gone over, and the pri- mary scaffolds selected, if this was not done at the time of planting. All undesirable growths should be pinched back. 4. At the first dormant pruning, the trees should be thinned to two or three primary scaffolds, properly spaced, and these scaffolds cut back lightly above the secondary branching. Care must be taken to leave the topmost branch longer in order that it may not be choked out. Branches on the trees in this group should not be cut to stubs except when abso- lutely essential. Figure 34 shows a branch of an apricot tree that had been cut to a stub at the previous pruning ; figure 35, the same branch after removal of the undesirable growths. Noticeable are the pruning wounds caused by cutting to "stubs," together with the poor crotch resulting. 5. During May of the second summer the trees are in the orchard, all unnecessary growth should be thinned out. Pruning Deciduous Fruit Trees 45 6. At the second dormant pruning, the tree will need only a thinning- out. 7. The same treatment should be given at the third as was given at the second dormant pruning. Trees in this first group handled according to the plan outlined above should produce a crop during the fourth season in the orchard and may Fig. 34. — A branch of an apricot tree cut severely to a stub at the preceding dormant pruning. Compare with figure 35, which shows the same branch after pruning. Unnecessary wood growth should have been removed early in May, and little pruning would then have been necessary through the winter. Better still, this branch should not have been cut back so heavily at the previous pruning. (From Bui. 313.) 46 California Agricultural Extension Service t ClR - 112 ood thereafter be treated as bearing. All this discussion presupposes soil conditions and careful cultural treatment. Training Young Apples, Cherries, Figs, Pears, Persimmons, European Plums, Prunes, and Quinces. — 1. The nursery tree should be cut at planting at a height of 24 to 30 inches above the around. 1 1 Hi 1 ; ^ 1 4 '/''■■•■ W'*-' *■ ,; ljfe& n '.t* ^ N ' : v* . '-» > "Wm.*«- *-» .-; 1 •- Fig. 35. — The same apricot branch as in figure 34 after pruning. Note the weak crotch and the large pruning wounds. Such severe pruning would not have been necessary if the tree had been cut lighter during the preceding winter or else unnecessary growth removed early in the growing season. (From Bui. 313.) Pruning Deciduous Fruit Trees 47 2. Soon after planting, the young tree should receive a coat of white- wash to prevent sunburn on the trunk. 3. During April, the tree should be carefully gone over, two or three primary scaffold branches being selected and all undesirable growths being pinched back. 4. At the first dormant pruning, the trees should be thinned to the two or three primary scaffold branches, properly spaced; and with apples, cherries, figs (certain varieties), pears, persimmons, and plums, these scaffolds should be cut back so that they will be 20 to 30 inches or more long. The primary scaffold branches of Mission and Adriatic figs may be left unheaded at this time. 5. During May of the second summer the trees are in the orchard, all unnecessary growth may be thinned out. If the trees are growing vigor- ously, a heading-back of the secondary scaffold branches, in addition to the thinning process, may be given to those varieties that were headed at the time of the dormant pruning. Under favorable conditions, this practice secures the usual second and third year's shaping during the second season. 6. With the exception of all varieties of the sweet cherry and of cer- tain varieties of the other fruits of this group, the pruning given during the second dormant season will consist of a thinning-out only. Because the sweet-cherry tree produces most of its new growth from terminal buds, it has a decided tendency to develop long, polelike branches if no heading is done. Growers usually cut back cherry trees moderately the first four or five years or until the framework is com- pleted. After the first few years, any further heading will delay the fruiting ; and the desired form can generally be attained by a thinning- out of superfluous growths. The cherry is slow in coming into bearing ; and just as long as new wood growth is encouraged by rather heavy cut- ting, the tree will make only shoot growth and will fail to develop fruit spurs. Under most conditions and in many varieties of apples, figs, pears, per- simmons, European plums, and prunes, heading-back one-year branches will have a decided tendency towards forcing all new shoot growth to arise from near the pruning cuts. If, on the other hand, these same branches are not cut back, the new shoots, except in certain varieties, will be well distributed up and down the previous year's growth. Notable exceptions to this rule are the Spitzenburg (Esopus Spitzenburg) apple and the Pond plum, which follow the habit of the sweet cherry in that new shoot growth arises from the tip of one-year wood whether or not this has been headed. 48 California Agricultural Extension Service [Cir. 112 The Bartlett pear, in most locations in California, will branch satis- factorily without heading. Because, however, this variety grows vigor- ously in soils well adapted to pears, a desirable practice in most districts is to head all primary scaffolds at the point where new branches are wished ; otherwise, considerable bending and breaking of the long one- year shoots may result. This heading of the scaffolds is usually continued until the framework of the tree is completed. 7. The same pruning as that outlined for the end of the second growing season should be given during the third dormant season and until the trees come into bearing. Figs, prunes, and European plums may be ex- pected to become profitable somewhat sooner than apples and pears. In general, the latter fruits bear sooner than cherries and walnuts. Varie- ties of the same fruit differ in the age at which they may be expected to reach profitable bearing : the Wagener apple, for example, is noted for its precocious fruiting, whereas the Northern Spy is notoriously slow in reaching productivity. 8. The Calimyrna fig, under favorable growing conditions, produces long branches, void of laterals. Heavy winter or light summer pruning may be used to shorten these so that the distances between laterals will be less. In winter, the shoots may be cut back to stubs about 20 inches long. As the tree begins to bear and as these shoots become less vigorous, less cutting-back will be required. The top should be thinned out so that it does not become too dense. Pinching off the tips of these long branches in the summer causes laterals to push out ; but this method should be prac- ticed only on vigorous trees, early in the summer. In pruning the Mission fig, the scaffold branches must be selected with especial care because of the acute angle usually formed at the junction of the new branch with the parent shoot. Splitting at this point often occurs with a heavy load of fruit. Trees in this second group, as designated above, may be expected to produce a crop during the fourth to eighth season and should thereafter be handled as bearing trees. All this discussion presupposes good soil conditions and careful cultural treatment. Training Young Pecans and Walnuts. — Trees of these species are cut to two or three buds at planting. A single shoot is selected during the first summer, all others being pinched back. This rapidly growing shoot should be staked so that it will not be broken or bent. At the end of the first summer, it may be anywhere from 4 to 8 feet tall. No heading, usually, will be necessary, since the walnut tree tends to throw a strong terminal growth in addition to a few lateral branches. A tall trunk is an advantage. Permanent lateral branches should be so selected that the Pruning Deciduous Fruit Trees 49 lowest certainly will not be closer than 4% feet from the ground — prefer- ably 6 feet. Branches developing below the desired level of the first per- manent scaffold should not be removed when they develop, but should A B C Fig. 36. — Walnut trees cut back to within 5 or 6 feet of the ground. A, If not trained they will frequently send out shoots along their entire length during the early summer. B, Frequently if the lower buds within 2 feet of the ground are allowed to grow, the upper 24 inches of the tree may remain dormant. C, If the lower buds are suppressed, the upper ones are forced into growth, and the framework of the tree is started in the upper 24 inches of the trunk. (From Bui. 379.) be pinched back at 15 to 18 inches in length. This leaf surface should be retained to help build trunk and root system and at the same time pro- tect the trunk from sunburn, but this temporary growth may be elimi- nated gradually over a two- to four-year period. Care should be exercised to select branches with a wide vertical spacing ; a distance of 2 feet be- 50 California Agricultural Extension Service t ClR - 112 tween branches seems advisable. Undesirably placed laterals may be pinched back in the summer and either cut back or removed entirely during' the dormant season. It may take two or three years to secure the desired framework, especially if the lowest branch is selected at 8 or 10 feet from the ground as some growers recommend. The tendency for most walnut varieties to spread and droop makes a high head desirable and does not eventually result in a higher tree. Permanent branches should not be developed from lateral shoots pro- duced during the same season as the parent branch. These laterals make an acute angle with the parent branch and split off easily. They should be removed entirely at the dormant pruning. All permanent branches should come from one-year buds. Such growths form a fairly wide angle with the parent branch or trunk, are more strongly attached, and will make a sturdier framework. In a coastal location, walnut trees planted under ideal conditions may be headed higher (5 or 6 feet) than suggested above (2 to 3 buds) and some laterals secured at the first dormant pruning. Where trees are thus handled, care must be exercised to pinch back all lower shoots during the first summer in order to force growth in the terminal parts (fig. 36). Effort should be made to reestablish an upward growing trunk, other- wise a weak, open, vase crotch will result. This method is not to be advised when trees are not well grown, when planting is late in the season, or when experience has shown that sunburn is a problem. PRACTICAL SUGGESTIONS FOR PRUNING BEARING DECIDUOUS FRUIT TREES Almonds. — The almond produces its fruit largely on short spurs, al- though some nuts are found on one-year wood, especially in certain varieties such as the Jordan and California. The spur, or fruiting branch, of the almond remains economically productive for about five years. For the sake of economy, the pruning of bearing almonds is usually restricted to the removal of limbs % inch to 1% inches in diameter. Little or no time is spent in thinning out one-year shoots except for the removal of water-sprouts, which are frequently abundant. This practice is probably satisfactory when the pruning is annual and when conditions are such that it results in sufficient new growth to renew the fruit spurs continually. Approximately one-fifth of the fruit wood should be replaced each season. Trees under ten or twelve years of age can be expected to make 9 to 18 inches of new growth over the tree as a whole, older trees 6 to 10 inches. Many old almond orchards do not make 6 inches of new growth each year, but the average production Pruning Deciduous Fruit Trees 51 would probably be increased if — by judicious pruning, fertilizing, and irrigating — this amount of growth could be induced. The pruning of trees lacking in vigor should consist of cutting back the tops to large lateral limbs and thinning the smaller shoots and fruiting branches. In general, the almond tree need not be thinned out quite so much as other trees because its foliage is rather sparse, so that light readily fil- ters through the branches. Furthermore, the almond is seldom, if ever, pruned to prevent overbearing, since the crop is not heavy enough to break any of the limbs and since the yield of the tree is more important than the size of the nuts. Because almonds are not picked by hand, the trees need not be kept so low as with most fruits. They should, however, be low enough so that all the nuts can be reached from the ground with a pole not longer than 16 feet. On very rich soils with abundant moisture, the trees may make an excessive wood growth at the age when they should come into bearing. Since pruning, except under conditions where carbohydrates are limit- ing, is one factor that tends to stimulate vegetative growth, the rational procedure in such a case is to stop pruning for a year or two. This prac- tice will tend to throw the trees into bearing and curb the heavy growth. After the bearing habit is once thoroughly established, pruning may be resumed. Apples. — Apples produce most of their fruit terminally on spurs that are found on wood two years old or older. The life of an individual apple spur is frequently as much as fifteen or twenty years, but in most or- chards, the period over which a spur bears often enough to be an im- portant factor in production is not over eight or ten years. Frequently these terminal-producing spurs fruit in alternate years. Unfavorable weather conditions may prevent most of the spurs from bearing in a particular year, and, in consequence, a heavy crop will be produced the next ; these trees will probably then be thrown into the habit of alternate bearing. There are certain notorious alternate-bearing varieties such as the Oldenburg, Baldwin, and Wealthy, which may firmly establish the alternating habit regardless of weather conditions. Often in California a spur elongates and sets a terminal fruit bud during the same summer that it is maturing fruit, in which case the habit of alternate bearing is broken. Although the major part of the apple crop is commonly borne on spurs, a smaller portion is produced on one-year wood, particularly with young trees of certain varieties such as the Gravenstein, Ben Davis, Jonathan, and Winesap. Varieties differ as to the part of the shoot on which the 52 California Agricultural Extension Service t ClR - 112 fruit is developed. Normally the fruit buds are borne either terminally or laterally near the apex. Varieties that produce an abundance of fruit buds on the one-year wood usually come into bearing at an earlier age and are more likely to bear annually than those that fruit entirely on spurs. A thinning-out of the branches to admit sufficient light to all parts of the tree is a prime consideration in causing new spurs to develop and in aiding those that already exist to bear regularly. Such thinning-out is also especially important in varieties having red fruit because an abundant light supply is necessary for the development of highly colored apples. Many varieties of apples tend to overbear, especially in the alternate years, so that the fruit requires much hand-thinning. The type of prun- ing to encourage annual bearing and reduce the amount of hand-thin- ning necessary is that which reduces the crop somewhat and invigorates the trees in the alternate years when they have a heavy set of fruit buds. The proper procedure is not only to thin shoots and branches, but also to thin out the spurs and to renew the long, much-branched ones by removing the older parts of the spurs and saving the newer — that is, to practice "spur pruning." Particularly with reference to the fruit buds and spurs, the pruning should be much lighter in the years following heavy crops, when the tree has comparatively few fruit buds. In general, the apple does not require heavy pruning. Because it bears largely on long-lived spurs, only about 10 per cent of which must be replaced each year, it requires somewhat less new wood growth than some other fruits. The young bearing apple tree should ordinarily make 10 to 20 inches of new wood growth each year, whereas for the older trees 6 to 10 inches is sufficient. This amount of new wood growth can ordi- narily be secured by cutting back to laterals, leaving a few of the one- year shoots intact. If, however, the wood growth shows a tendency to drop below the minimum amounts mentioned above, heading back the laterals that are left after thinning may be necessary to secure the proper vigor. The apple powdery mildew, which has done considerable damage to the apple orchards in California, particularly in the humid coast regions, can be largely controlled by proper pruning in conjunction with spray- ing. The pruning treatment in this respect consists in removing the diseased shoots and spurs at the regular dormant pruning, which elimi- nates the sources of holdover infection. Mildewed shoots are easily rec- ognized by their gray or silvery appearance. The undesirability of removing large limbs has already been pointed out (p. 41) . It is especially dangerous, however, to cut off main branches Pruning Deciduous Fruit Trees 53 in damp coast districts, such as the Pajaro Valley. When limbs more than iy 2 inches in diameter are removed, a wood and bark disease known locally as "sappy bark" is liable to develop. This serious malady often travels down the limb from a large wound, eventually reaching the trunk and killing the tree. Disinfecting and painting the wounds has not always proved effective in preventing the disease. Apricots. — The apricot produces most of its fruit laterally on spurs that are usually not productive for more than three years. A relatively small portion of the crop is produced laterally on one-year shoots. Since the fruit-spur system of the apricot is short-lived, the pruning treatment should be designed to cause its continual renewal. Young bear- ing apricot trees should make 15 to 30 inches of new growth each year. On older trees, the desirable length of new growth ranges from 10 to 24 inches. The peach and Japanese plum are probably the only fruits that ordinarily require a heavier pruning than the apricot in order to pro- duce sufficient new growth for continued profitable production. Particular care should be taken not to allow the branches to become too long, willowy, and unbranched. As the tree becomes older and only a short growth follows a thinning system of pruning, a severer type of cutting may be needed to maintain the vigor of the tree. As the tree becomes older, the continuance of a comparatively light system of pruning, especially in the absence of adequate soil moisture, will usually slow down the wood growth and consequently diminish the yield. In sections subject to brown rot, effort should be made to remove in- fected spurs and shoots, because these produce spores of the fungus the following spring and make control by spraying more difficult. Sweet Cherries. — Sweet cherries are borne laterally on long-lived spurs which are economically productive for ten or twelve years. Be- cause of this persistence of the fruit-spur system, the sweet cherry needs less renewal wood than almost any other deciduous fruit. If the trees have been properly trained and brought into bearing, little pruning is necessary to keep them productive. Whatever pruning is done, however, should be annual and severe enough to renew approximately 10 per cent of the fruit-bearing area each year. As the sweet-cherry tree naturally grows upright, one should give it as much spread as possible by retaining the outward-growing shoots and removing the upright ones. This procedure is especially important with such upright-growing varieties as the Lambert and Black Tartarian. The Royal Ann (Napoleon) naturally assumes a spreading habit with age. Certain cherry growers have kept their trees low by doing little or 54 California Agricultural Extension Service i Cm - n2 no pruning during the earlier years and thus forcing them into rather precocious fruiting and allowing the weight of the crops to bring about the desired spread. Careful judgment, however, must be used in follow- ing such a plan. The cherry tree is particular as to the conditions under which it will thrive : it is susceptible to drought and to excessive soil moisture. The reinvigoration of weak trees cannot be achieved by the mere adoption of a rational pruning method. To keep a bearing cherry orchard vigorous, emphasis must be laid on proper soil conditions. When cherry trees are cut back into older wood, either to lower the trees or to stimulate the wood growth, care should be taken to cut to a lateral wherever possible. Trees showing much die-back of the outer branches can sometimes be rejuvenated by rather severe pruning. It should be stressed again, how- ever, that soil conditions must also be improved. Figs." — Growers of the Adriatic and Mission varieties of the fig should remove annually the lower limbs that interfere with cultural practices and should administer a top pruning to remove crossing and interfering branches and sunburned or dead wood. The pruning of bearing Calimyrna figs will vary with the annual amount of growth, consisting merely of a thinning-out if the new wood growth is not excessive, a thinning-out and a heading-back if the new growth is vigorous. The thinning is to open the tree, whereas the heading- back (in vigorous trees) is to secure more compactness of the new fruit wood. It is perhaps advisable to cut out occasional large branches at the top of the tree rather than to stub back many smaller ones. The Kadota is pruned to secure a low, spreading tree. The flat top is produced by cutting the inside branches shorter than the outside ones. Each winter, vigorous new branches should be cut back to about 15 inches, and thinning should be done to admit light to the lower branches. A low tree facilitates picking (fig. 37) . Terminal-bud pruning in early spring is occasionally practiced on the Turkey variety of fig. The terminal bud of fruiting branches is removed, which causes lateral fruit buds to develop earlier. Another practice with the Turkey in early districts is to prune as soon as the first crop has been harvested, in order to produce new wood for a more abundant crop of late figs. In southern California, along the coast, the usual heavy winter pruning produces heavy crops. Caprifigs are often headed back to keep the tree low in order that fruits may be picked easily. This heading is generally less severe than with the 3 A more detailed account of fig pruning may be found in : Condit, Ira. Fig culture in California. California Agr. Ext. Cir. 77:1-69. 1933. Pruning Deciduous Fruit Trees 55 Kadota. Somewhat different methods and times of pruning are used with the different varieties of caprifigs, largely according to the time of fruit- ing and the amount of crop desired at a particular season. Peaches and Nectarines. — The fruiting habit of the nectarine is iden- tical with that of the peach. Probably no other fruit responds to proper pruning and declines with neglect so readily as the peach, largely because it bears its crop almost *: ■^ Fig. 37. — Low-spreading Kadota trees are secured by pruning the outside branches long and the inside branches short. This shows a tree as pruned at the end of five growing seasons. (From Ext. Cir. 77.) entirely on one-year shoots. Only occasionally is fruit found on spurs, and these are very short-lived. For this reason, peach trees must be pruned more heavily than most other fruits in order to produce sufficient fruit-bearing wood each year. From 20 to 40 inches of growth over the tree as a whole is not excessive for young bearing trees. Older trees may be expected to produce each season an abundance of shoots from 12 to 30 inches long. The bearing area of the peach is carried higher and higher each year, which tends to leave long stretches of nonf ruiting branches that are sub- ject to sunburn and decay and that serve only as a connection between the fruiting periphery of the tree and its sources of water and mineral nutrients — the roots. Because the foliage is dense, it is difficult to main- tain a satisfactory distribution of the fruit wood in the interior of the tree. Care must be taken to thin the trees out so that adequate light may reach all parts and fruiting branches be retained on the lower limbs. If this detail is not carefully managed, the result is a "leggy" peach tree 56 California Agricultural Extension Service [Cir.11! with sunburned branches and with practically all new growth confined to the periphery. Hanging shoots and branches, sometimes called "hangers," are par- ticularly desirable for fruit bearing on peach trees and should be encour- aged. Care should be exercised, however, to prevent these from becoming ■\\f\ Fig. 38. — Seven-year-old Elberta peach tree before pruning. Note the vigor- ous new wood growth which, however, is not excessive. Compare with figure 39 after pruning by thinning. This tree has been well pruned during preceding seasons. (From Bui. 386.) too long through the addition of a certain amount of growth each year. Frequently one can shorten and renew such shoots by cutting back to a strong new lateral. Fruit on these hangers is borne on relatively short annual growths and sometimes on spurs. Seldom, in California, does a peach tree fail to set enough fruit buds for a heavy crop. In fact, one perplexing problem in the pruning of bearing peach trees is to determine how much fruit wood should be left to blossom and mature fruit. After the trees have been thinned of the superfluous larger branches and the desired form has been secured, the question arises how best to reduce the fruit buds so that the crop will be well distributed and will not impose too heavy a task at the thinning season. Generally speaking, one can more economically reduce the crop with the pruning shears during the dormant season than entirely by Pruning Deciduous Fruit Trees 57 hand-thinning after the fruit is set. To attempt to thin with the pruning shears so that no hand-thinning will be necessary to secure the desired size and quality is liable, however, to reduce the total tonnage so greatly that the practice will not be economical. This reduction of the fruit wood may be accomplished by thinning-out Pig. 39. — A seven-year-old Elberta peach tree well pruned by thinning out. Compare with figure 38 before pruning. Note the large amount of growth re- moved. This tree has been pruned for four consecutive years by thinning — no cutting to stubs. (From Bui. 386.) or heading-back or by combining these two methods. Care must be taken not to head the new shoots on varieties that bear only at the tip or on the outer half of the shoot, especially when the set of fruit buds is light. This method of fruiting is characteristic of such varieties as the Tuscan and Phillips Cling peaches. On the other hand, the Elberta, Muir, Alexander, and Early Crawford are typical of the varieties that bear rather uni- formly throughout the length of the shoot. With the latter varieties, heading of the fruiting twigs may be entirely feasible — in fact, desirable. In most instances, the proper amount of fruit wood should be ob- tained by : 1. Thinning out the unbranched one-year fruiting shoots. 2. Cutting back lightly or moderately to laterals the fruiting shoots that are branched. 58 California Agricultural Extension Service t ClR - 112 3. Thinning out the remaining laterals on these branched shoots. 4. Heading back the fruiting shoots which are thus left, where experi- ence has shown this practice to be desirable, from the standpoint of thinning the crop or securing new wood growth for the crop of the fol- lowing year. Where possible, it is well to cut to the brownish-colored, stocky laterals rather than to slender, reddish shoots, because the former are better adapted to continue the framework of the tree and generally produce fruit of somewhat higher quality. In cutting back to a lateral that is likely to bear fruit the following season, one should leave a short stub just above the lateral — % or % i nc h long — to prevent the lateral from being broken off by the weight of the fruit. Figures 38 and 39 show a young bearing peach tree before and after pruning. This tree has responded well to a pruning consisting entirely of thinning and cutting to laterals. Pears. — In fruit bearing, the pear is almost identical with the apple ; hence suggestions regarding the pruning of the apple apply here with equal force. The pear of course has varietal characteristics just as the apple has : some varieties tend to come into bearing earlier than others ; likewise, varieties such as the Bartlett, Winter Nelis, and Angouleme tend to produce much of their crop, especially during the early bearing years, at or near the end of one-year wood. The tendency towards alter- nate bearing in pears is less pronounced than in the apple ; the fruit spurs are generally somewhat shorter ; and the tree is more upright in habit of growth. Figure 40 shows an ideally shaped pear tree. Figure 41 illustrates the pruning of a nine-year-old Bartlett. Under favorable soil and moisture conditions, neglected pear trees sometimes make an exceptional develop- ment (fig. 42) ; a system involving little or no pruning is not to be gen- erally recommended, but may occasionally be advantageous on very rich and moist soils, by increasing yields and by decreasing vigorous vegeta- tive growth, which is susceptible to the ravages of pear blight. Persimmons? — The pruning of bearing persimmon trees should be limited to the renewal of the fruit wood. Since the fruit is borne on the current season's growth, sufficient thinning should be given to insure vigorous growth each season from the secondary scaffold branches. Be- cause of the general tendency toward vigorous growth, care is required 4 For further details, see: Ryerson, Knowles A. Culture of the Oriental persimmon in California. California Agr. Exp. Sta. Bui. 416:44-45, 47-48. Revised 1927 by Robert W. Hodgson. (Out of print; may be consulted at many city and county libraries in California.) Pruning Deciduous Fruit Trees 59 to thin sufficiently to admit light. Otherwise, the interior fruit wood will die and all the crop will be borne on the outer parts of the tree, materially decreasing the possibilities of the crops and augmenting the danger of breakage. All cuts should be made to laterals in order to avoid heading i*tn 3 ■I Y ; V / JL* %& Fig. 40. — A well-pruned ten-year-old Glou Morceau pear tree. Note the size of the few scaffold branches. An ideal framework capable of supporting immense crops without breakage. (From Bui. 386.) or "stubbing," which is objectionable. Water-sprouts on the trunk and main branches should be rubbed off except when needed to fill in spaces opened by breakage. Excessive cutting and stubbing results largely in the production of vigorous vegetative growth and in failure to fruit. Old, 60 California Agricultural Extension Service [Cir. 112 neglected trees can be rejuvenated by a rather vigorous thinning and cut- ting-back to laterals and by shortening the main branches to force out laterals where, through long neglect, all interior fruit wood has dis- appeared. Japanese Plums. — Two general classes of plums are commercially cul- tivated in California — the Japanese and the European. The former Pig. 41. — A nine-year-old Bartlett pear tree before and after pruning. This tree has been con- sistently pruned rather lightly. Compare with figure 42 of an adjoining tree not pruned for five years. The photographs were taken at the same distance from each tree. (From Bui. 386.) includes only shipping varieties ; the latter, both shipping plums and prunes. Since the fruiting habit and the pruning of these two classes are somewhat different, the discussion may well be divided into two parts. Japanese plums are, as a rule, borne laterally upon short, thick spurs. The spurs are found mostly on wood two to six or eight years of age. The life of a spur varies from five to eight years. A minor portion of the crop is borne laterally on one-year wood, the fruit being produced in general at the basal part of the shoot. The fruit-bearing habit of the Japanese plum resembles that of the apricot, the principal difference being that the spurs on the plum live somewhat longer. Naturally, therefore, the pruning of these two fruits Pruning Deciduous Fruit Trees 61 is much alike. The fact that the spurs of the Japanese plum are longer- lived would lead one to conclude that these plums should be pruned some- what less severely than the apricot, there being less necessity of replacing the fruit wood with new shoots. The Japanese plum is, however, prolific ; and as only large fruits are commercially valuable, the trees must be pruned rather heavily to reduce the fruit crop and at the same time in- Fig. 42. — A nine-year-old Bartlett pear tree before and after pruning. Deliberately left impruned for the five years preceding. Note the splendid development of fruit wood and framework branches. Compare with figure 41, of an adjoining tree pruned lightly. Besides increasing enormously in size, this tree has produced six to eight times as much fruit as the lightly pruned tree. This illustration is introduced not in the way of recommendation but merely to emphasize the greater development secured by little or no pruning as long as the tree makes sufficient new wood growth. (From Bui. 386.) (luce sufficient new wood growth. As a result, therefore, the severity of the pruning of these two fruits should be closely similar. The plum should be so pruned that some 10 to 24 inches of new wood growth annually is secured on young bearing trees and 10 to 12 inches on older ones. In habit of growth, the several varieties differ considerably. Some, such as the Burbank, are rather low-spreading growers ; and even after the trees come into bearing, attention must be paid to diverting the growth into the more upright branches. The Wickson, Kelsey, and Santa Rosa, on the other hand, are examples of varieties that make a very nar- row, upright growth and require careful pruning for the proper spread. 62 California Agricultural Extension Service [Cir. 112 European Plums. — The fruit spurs of the European plums differ from those of the Japanese, being longer, more slender, and frequently branched. Old spurs — or, as they are sometimes called, "fruiting brush" — may reach a length of 2 or 3 feet, whereas the spurs of Japanese plums rarely exceed 2 or 3 inches. The pruning of European shipping plums closely resembles that of Japanese plums, but it is for two reasons less severe. Since European plums do not tend to overproduce as do the Japanese, a light pruning is sometimes necessary to favor fruit-bud formation in them, rather than a severe pruning to reduce the quantity of fruit buds as with the Japa- nese. Furthermore, a relatively larger proportion of the fruit of the European plum is borne on spurs. Keeping these facts in mind, the grower may handle the European shipping plums much the same as the Japanese plum and the apricot. Mature plums that contain enough sugar to dry without fermenting are called prunes. The fruiting habit of prunes is identical with that of European shipping plums. Since, with the exception of the Sugar and Burton varieties, the fruit is not usually thinned or picked from the tree, prune growers have made no great attempt to keep their trees within bounds. The relation of the cost of pruning and spraying to the height of the tree should not, however, be overlooked. The treatment commonly given prune trees in California consists in a rather severe thinning of both the fruiting brush and the larger limbs. Often this treatment is given only irregularly and infrequently. Vigor- ous new shoots arise near the cuts, which necessitates a severe pruning the following season. Two or three years may elapse before trees thus heavily pruned again settle down to good production. It should therefore be emphasized that the cutting of prune trees should be done regularly but in most cases should be merely a light thinning-out of the shoots, old spurs, and smaller branches (fig. 43). Often the hanging branches are cut back to upward- and outward-pointing limbs in order to keep the tree well shaped. From an economical point of view it is fortunate that few cuts less than % inch in diameter are necessary to encourage the growth of sufficient new wood. An average yearly extension of the leading branches of 9 to 18 inches is adequate for young bearing prune trees. Older trees should be expected to make at least 6 inches of growth each summer. Because of the more compact fruit-spur system of the Im- perial variety, more detailed and finer pruning must be given than is generally accorded the French variety, the one commonly considered when prunes are discussed. Usually, in the older prune orchards that have received little pruning, Pruning Deciduous Fruit Trees 63 the bearing area is a thin shell on the periphery of the tree : a branch 8 feet long, for example, often has all its fruit spurs on 2 or 3 feet at the terminal end of the branch, the rest of the branch being bare and unpro- ductive. This concentration of the bearing area at the ends of the branches is generally caused by insufficient thinning, resulting in a shading out of the interior and of the lower fruit wood. The fruit spurs, if not killed, ; Fig. 43. — Thirty-year-old French prune tree pruned by removing a few of the larger branches and thoroughly thinning the fruiting brush. (From Bui. 386.) are often long, slender, and unproductive, in contrast with the shorter, stockier, fruit-producing spurs to be found on the outside of the tree. Such shaded, willowy spurs produce small fruit and are short-lived. Ob- viously the corrective treatment for such a condition lies in an adequate thinning-out of the smaller branches, where the tree has been properly trained, and even in the removal of a few larger branches if the frame- work is crowded. A word of caution is necessary. Since the prune tree is highly susceptible to sunburn, good judgment must be exercised in thin- ning out larger branches in the bearing trees. The Sugar prune behaves somewhat differently from the other varie- ties commonly grown in California. Like the sweet cherry, it has a pro- nounced tendency to make most of its new growth on the tips of the 64 California Agricultural Extension Service t ClR - n2 previous season's shoots. In several different localities it has proved to be an alternate bearer, and since the wood is brittle, the branches frequently break during the year of heavy production. In the alternate years, then, when the trees have a heavy set of plump fruit buds, they should be pruned heavily, new shoots cut back especially to prevent the formation of long polelike branches, and the fruit wood thinned out. Thinning of the fruit, if done early enough, may possibly tend to correct this alternat- ing habit. In the off year, when the set of fruit buds is rather light, com- paratively little pruning, especially in the way of limiting fruit buds, should be done. Quinces. — The fruit of the quince is borne terminally on compara- tively long current-season's shoots, arising from lateral and terminal buds on one-year wood. Since fruit buds are produced only on one-year wood, the grower must attempt to stimulate such amounts of vegetative growth that the fruit wood will be renewed annually. As experience has shown, however, heavy production can usually be secured without a se- vere pruning. In fact, quinces sometimes continue to bear good crops of large-sized fruit when very little pruning is practiced. It seems best, nevertheless, to give a pruning that will stimulate 10 to 24 inches of new growth each year on young, and 9 to 18 inches on older, quince trees. The pruning should consist mainly of a thinning-out and heading-back to laterals. Occasionally, however, one must prune more severely to in- duce sufficient new growth. Walnuts. 5 — Walnut trees should be moderately pruned every year rather than severely cut at three- or four-year intervals. Pruning should be done during the dormant season — December through February. Need for pruning a bearing walnut tree may be judged on two factors — first, density of shadow cast by the tree during midsummer when leaf develop- ment is maximum, and, second, the vigor of fruiting branches throughout the central area of the top. If the shadow is practically complete, with little or no sunlight reaching the ground, the top may be judged as too dense and in need of thinning. In such a case, inside fruit wood will lose its leaves during the summer and will be found weak or dead at pruning time. If, on the other hand, what should be normally vigorous inside fruit wood grows with great rapidity and becomes large, too much sun- light is coming through. Fruit wood should be maintained on larger limbs. Long bare branches tend to sunburn, become weak and spindly, and are liable to break. Top thinning may require the elimination of one or more large branches if 5 A more detailed account of walnut pruning is given in : Batchelor, L. D. Walnut culture in California. California Agr. Exp. Sta. Bui. 379:39-44, 69. Revised 1936 by L. D. Batchelor and O. Lee Braucher. Pruning Deciduous Fruit Trees 65 too many were left when the tree was small or if it has not been con- sistently primed. Thereafter, and for a normal animal program, the removal of a few (2 or 3 to 6 or 8, according to the size of the tree) branches l 1 /^ to 2 inches in diameter should maintain sunlight distribu- tion and keep inside fruit wood vigorous. Interfering or cross branches, weak or dead wood, should be cut away. Low-hanging branches which might interfere with cultural operations may be eliminated if desired. Proper pruning of individual trees cannot prevent the crowding and interfering of whole trees which have grown too large for the space pro- vided at planting time. There should be a minimum of 4 to 6 feet between the perimeter of trees when their branches are weighted down with fruit and foliage. Crowded trees shade each other, and the shaded portions become progressively weaker, produce a poor quality of nut, and eventu- ally die. To remedy this condition, whole trees should be removed. One satisfactory method of tree thinning is to remove every other tree in every alternate row, in a diagonal. The trees destined for removal should be pruned in such a way as to favor and protect the permanent trees. The adoption of such a system several years prior to actual removal will result in maximum annual tonnage. SUMMARY OF FACTS TO BE KEPT IN MIND WHEN PRUNING YOUNG NONBEARING TREES 1. Young trees should have their tops cut back at planting in order : a) To balance the loss of roots removed in digging from the nursery. b ) To form a low head for future profitable orchard management. 2. Sunburn may be controlled, in part, through shading by means of low-headed trees. 3. Only three main, or primary, scaffold limbs are desirable, and these should be spaced 6 to 8 inches apart at the points where they arise from the trunk (p. 17). 4. Nursery lateral branches, if properly distributed, may be utilized in forming the head of the tree at planting time. 5. Five to seven primary and secondary scaffolds at 5 feet from the ground are sufficient for a mature tree (p. 17) . 6. After securing the desired number of scaffold branches, together with the proper spread, it is useless, except with certain kinds and varie- ties, to head back the young tree again. 7. Lightly pruned trees have stockier and stronger branches than heavily pruned trees. 66 California Agricultural Extension Service [Cir. 112 8. The more lightly a tree is pruned, the greater the development (p. 10) of both top and root. 9. Cutting any branch or part of a tree heavily lessens total growth in that branch or part. Pruning any part lightly increases the total growth in that part (p. 19). 10. Lightly pruned trees come into bearing one to three years earlier than similar trees that have been heavily pruned. 11. Early bearing does not interfere with future productivity. 12. Summer pruning tends to be weakening and to result in somewhat smaller trees. Under certain conditions, however, it may be advisable. SUMMARY OF FACTS TO BE KEPT IN MIND WHEN PRUNING BEARING TREES 1. The total amount of new growth that the tree makes, considering the crop produced and the conditions under which it is grown, is the best criterion by which to judge whether or not the pruning has been of the proper severity (p. 34). a) If the resultant new growth is longer than seems desirable for a given kind of tree under given growing conditions, then the previous pruning was too severe. b ) If the new growth has been inadequate, the cutting was too light, and a heavier pruning program should be adopted unless the sparse growth has resulted from nonavailability of carbohydrates. 2. The pruning should include adequate thinning-out of the fruiting shoots ; and this thinning should be followed, where necessary, by a thor- ough hand-thinning of the fruit (p. 41) . 3. The tree should be thinned sufficiently to admit an adequate supply of light (p. 41). 4. All interfering branches, dead wood, and diseased parts should be removed. 5. The larger limbs should be spaced far enough apart throughout their length to have ample room for developing the desired fruiting branches and spurs. 6. The trees may be kept from becoming too high by regularly cutting back the tallest branches to strong, outward-growing laterals. 7. All branches should be cut off close to the limb from which they arise, leaving no stubs (p. 41). 8. Ideal shape, height, and distribution of fruit wood cannot be secured unless the trees are planted far enough apart to develop normally. Cali- Pruning Deciduous Fruit Trees 67 fornia fruit growers have tended to plant their trees too close together for normal development. 9. Careful pruning, though important, will not compensate for the neglect of fertilization, cultivation, spraying, fruit thinning, irrigation, or other phases of orchard management. ACKNOWLEDGMENTS The author is indebted to V. F. Blanchard, M. H. Kimball, and E. F. Serr of the Agricultural Extension Service for suggestions concerning the pruning of walnuts. 20m-10,'39(1238)