UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA PLANTING AND THINNING DISTANCES FOR DECIDUOUS FRUIT TREES F. W. ALLEN BULLETIN 414 November, 1926 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA 1926 Digitized by the Internet Archive in 2012 with funding from University of California, Davis Libraries http://www.archive.org/details/plantingthinning414alle PLANTING AND THINNING DISTANCES FOR DECIDUOUS FRUIT TREES F. W. ALLENi INTRODUCTION In planting an orchard, one of the first questions to be settled is the amount of space to be allotted to each tree for root and top development. This requires a decision as to how far apart the rows shall be and the distance between the trees in the rows. Aside from the number of trees that can be safely planted on an acre of ground, certain other practical considerations enter in, such as the best arrangement of the trees for convenience in cultivating, irrigating, brush burning, spraying and harvesting. A closely related problem is the question of what shall be done with orchards that are found to be too closely planted. In the first instance the planter strives to avoid a mistake, while in the second he tries to correct one. Both topics will be discussed in the succeeding pages. The information on which this discussion is based was secured from an orchard planted on the University Farm at Davis for the purpose of studying planting distances, and from careful observations made in a number of established orchards in different parts of the state. EXPERIMENTAL ORCHARD AT DAVIS The experimental orchard at Davis was planted in February, 1915, and consisted of the following fruits : Royal apricots, Climax and Pond plums, Bartlett pears, Royal Ann cherries, Elberta peaches, and French prunes, the trees being arranged in blocks, with each block representing a different planting distance. The planting dis- tances ranged from 12 x 12 feet to 36 x 36 feet, the number of trees per block varying from 302 in the former instance to only 33 in the latter. The total number of trees planted was 668, but as each block was provided with guard rows so that all trees used for record purposes were surrounded with other trees of their kind, only 354 remained on which to keep growth and yield data. Table 1 shows the number of trees in each block. This orchard was valuable chiefly for studying the comparative growth of trees under various conditions of planting, ranging from 1 Assistant Pomologist in the Experiment Station. UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE 1 Planting Plan and Number of Trees of Each Fruit Planted in Different Blocks Planting distance and kind of fruit Number of trees planted Number used for record purposes Planting distance and kind of fruit Number of trees planted Number used for record purposes 12x12 feet: 45 25 25 45 36 36 40 24 16 12 24 24 28 24 15 9 9 15 15 18 15 24 12 12 24 24 24 24 15 9 6 15 15 15 15 8 4 4 8 8 8 8 24x24 feet: Apricot Plum (Japanese) Plum (European) Pear 12 6 9 12 12 15 12 9 6 6 9 9 12 9 9 12 9 6 2 4 6 Peach 6 6 Prune 6 16x16 feet: Apricot 30x30 feet: Apricot Plum (Japanese) Plum (European) Pear 4 2 Plum (European) Pear , 2 4 4 4 4 20x20 feet: Apricot 36x36 feet: Apricot 4 4 4 Pear a badly crowded condition to the opposite extreme where they were so far apart that there could be little or no competition for moisture, soil nutrients, or light. Unfortunately, the plans made by the orig- inator of the experiment did not provide for as many trees in the widely planted blocks as there should have been. Through the vicissi- tudes of subnormal rainfall and shortage of water for irrigation purposes during two or three seasons when the trees were coming into bearing, it became apparent that those in the crowded blocks in particular were being subjected to unusually severe conditions and that they were suffering accordingly. Radical thinning by taking out trees was resorted to, but the apricots and peaches did not recover their lost vigor. Even those having plenty of room showed continued signs of drought injury. Incidentally, this experiment taught two lessons: First, that it is hazardous to allow young trees to suffer for water to the extent of slowing down their growth and, second, that certain trees, at least, do not recover after once having been injured from overcrowding during a period of dry years. BUL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES FACTORS INFLUENCING PLANTING DISTANCES Horticultural writers have not always been uniform in their advice as to the amount of space trees should be allowed or as to their exact arrangement in the orchard. Even experienced fruit growers in a limited district may not be entirely in agreement as to how the trees should be spaced or the total number that may be allowed to the acre. There are certain basic considerations which need to be taken into account in deciding planting distances. Even under best conditions for normal growth not all fruit trees attain the same size at maturity; moreover, growth habits of the different species and varieties as to size and shape are quite varied. Some are normally tall and slender, at least for many years, while others are spreading in their habit of growth from the beginning. Sweet cherries, for example, in good soils often attain a height of thirty-five feet and a branch spread of perhaps twenty feet ; while sour cherries are rarely over twenty feet high and have a branch spread not exceeding twelve or fifteen feet. Pears are noted for being upright in their growth, while apples and apricots are generally wide-spreading. Some trees when grown on certain rootstocks such as the Bartlett pear on the quince are also, normally, dwarfs. The soil, whether deep or shallow, has much to do with the size of a tree of a given species or variety. On shallow soil even trees that are normally large, if they survive, are apt to be small. However, on such soils where the roots are unable to penetrate deeply, they are apt to range widely in search of both food and moisture so that trees should not be unduly crowded simply because it is known that they will not attain large size. The moisture supply in the soil is perhaps the most important single factor affecting the growth of fruit trees. Even on the most productive soils, trees will make a small growth, soon lose their vitality, and gradually die if allowed to suffer for water. Evidence of this has been noted in non-irrigated orchards, especially those where small fruits are interplanted between the trees. Tree sizes can be regulated to a considerable degree by pruning. Heavy annual pruning consisting of shearing back the new growth tends to keep the trees small. This type of pruning may adapt them to certain planting distances, whereas if they were handled by the so-called "long pruning," they would inevitably require more space. There are really two considerations : the welfare of the roots as regards a proper moisture supply, and the welfare of the tops. If unduly UNIVERSITY OF CALIFORNIA EXPERIMENT STATION crowded, the tops may not secure the necessary amount of sunlight ; moreover, harvesting, spraying, and other field operations may be hampered. Hoot growth, too, is influenced by heavy pruning. 2 Heavy shearing of the branches annually tends to restrict the growth of the roots. Again, the purpose of the orchard may have an influence on the spacing of the trees. Most orchards are planted with the idea that the trees are to be permanent and hence they should be given a suffi- cient amount of space for the best development of both tops and roots over a long period of years. Under certain circumstances it may seem necessary to plant a temporary orchard in which the trees may be set very thickly. They are brought into bearing early and given little or no pruning in order to secure a few heavy crops ; then, when their vigor begins to decline, all are removed from the land. In times of high prices for a certain fruit it may be good business to give the trees a reasonable amount of space in which to develop but yet plant the maximum number of trees to the acre. Such growers, of course, should be willing to take the risk of injuring the trees by slight crowd- ing. The returns from the orchard may justify this procedure, although the orchards should be regarded as only semi-permanent. A single adverse season as regards water supply may result in severe or fatal injury to a high percentage of such trees, whereas under favorable conditions of moisture and with first class cultural attention they may survive and be useful for many years. Table 2 may be useful in computing the number of trees required for any given area. TABLE 2 Number, of Trees Eequired per Acre Planting distances, in feet Number of trees per acre square or alter- nate planting* 18x18 134 20x20 108 22x22 90 25x25 70 27x27 59 30x30 48 35x35 35 40x40 27 50x50 17 60x60 12 * Figures are exact only for a multiple of acres. For hexagonal planting add 15 per cent to above figures; for quincunx planting add 100 per cent. 2 Chandler, W. H. Eesults of some experiments in pruning fruit trees. Cornell Univ. Agr. Exp. Sta. Bui. 415:5-8. 1923. BuL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES RELATION OF PLANTING DISTANCES TO THE GROWTH AND FRUITING OF THE TREES Tree growth. — The accompanying chart, figure 1, illustrates the total size of the experimental trees on the University Farm and also the annual rate of growth as measured by increase in trunk diameter. During the first three years after planting, differences in growth between the trees planted at 12 feet and those planted at 30 or 36 feet apart are small and of no special significance. The fourth season, 1918, being unfavorable on account of only ten inches of rainfall between September, 1917, and September, 1918, and no irrigation water available, all trees made less growth than either the year pre- vious or the one following. At this time the apricots and peaches planted at the wider distances were of decidedly larger size. During 1919 all trees made a uniform gain except the apricots which again made a relatively small amount of growth in the closely planted blocks. Beginning with 1920, another dry season, the dwarfing effects of close planting were even more apparent. 3 It will be noted that the effects of the varying distances were much more marked with the apricot, peach, and cherry than with the plum, prune, and pear. The growth for the pear is particularly uniform in each of the planting distances during the entire ten-year period. The relative amount of space available for the development of the tree-top or spread of branches has been correspondingly striking. Peaches and apricots, naturally of a spreading habit, were by 1918 in the closer planted blocks being forced into a smaller, more upright habit of growth, as illustrated in figure 2 and figure 5A. The amount and vigor of the new wood produced also gradually became less until 1922, when, in a much weakened condition, 50 per cent of the trees were removed. Although to a somewhat lesser extent plums, prunes, and cherries were likewise influenced under similar conditions, and thinning was also necessary in order to prevent the gradual dying of the trees. Pears, naturally of an upright habit, have been the least affected in the character of their growth. Crowding has produced smaller and perhaps slightly weaker trees, but the general character of growth has been little influenced. Fruiting habits. — As the branches of the peach and apricot when crowded were forced upward to secure sunlight, the new wood bearing all the fruit of the peach and a portion of that in the apricot became more limited and higher up in the tree. With a gradual dying of s Increase in size of trees planted at 12 and 16 feet during and after 1922, primarily the result of thinning. UNIVERSITY OF CALIFORNIA EXPERIMENT STATION /2 a 12 16 a 16 20a20 2Aa24 30a30 36a36 /2a/2 16 a 16 20a20 24 a 24 JO A JO /2a/2 16 a /6 20a20 ^24 a 24 "b joaSO 19/4-15 J /9I6 T /9/4-/5X/9/Q T ,9/7 I /$/& \ /9)9~ I9M-I5\/9IS I ,9/7 I A? I /9/9 \2Q\ /92/ 1 2£ I 1 923 \ \ 12 a /2 ^ /6a, 6 U 20*20 I ^ 24x24 SO-aSO S6aJ6 iwr 1 1 1 \I8VI9 || \\23\I924\ ,1.1 'M 1, I IJZD XX XL -~TT\ [I I XjOL Royal Apricots ) i I L nx /9PO | t92l | !9Cr 1 ?J I -?4 | ,914-/5 \ ,9/6 | /g/7 |/<9|/g ^Q| | I I I I I I! f [ \ I I CZXIElberta Peaches X=X \ I J (==n ,9,4-/5 I 79/6 | /5y7 /9/ | /g ,2 ,6 >, 6 20a£0 2Aa£4 30x30 3&i36 ,9/4-,5\/6 | /9/7 \ /S \ /9/9 ]2Q\ ,92/ \ ,922 ~\/9ej\/9•.: ■ Fig. 4. — Eight-year-old Elberta peach trees. A, two years after thinning from 12 x 12 feet to 24 x 24 feet. Only one tree out of four of any value. B, trees planted 20 x 20 feet. Half of the trees in fair condition, others very weak. C, trees planted 24 x 24 feet. All in good condition. Compare with trees in A. 16 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION Fig. 5. — Eoyal apricot trees. A, apart. B, same trees second season after thinning to 24 x 24 feet, parable trees planted 24 x 24 feet. Compare size and vigor. trees six years old standing 12 x 12 feet C, com- BUL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES 17 the remaining trees to stand 48 x 48 feet on the square but only 34 feet on the diagonal. Though the branches are touching in the close or diagonal direction, the trees produce large crops. An additional 20 acres of 10-year-old almonds will in a few years be thinned in like Fig. 6. — Eight-year-old Climax plum trees. A, trees thinned several months before photographing from 12 x 12 feet to 24 x 24 feet. B, trees originally planted 24 x 24 feet. Compare size and vigor. manner. Mr. ~Boyce is of the opinion that he would in all probability plant and handle another orchard in the same way. Mr. William D. McKenzie, an extensive grower of prunes and pears at Monticello, believes double planting to be an economic 18 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Fig. 7. — Eight-year-old Boyal Ann cherry trees. A, thinned several months previous to photographing from 12 x 12 feet to 24 x 24 feet. B, trees planted 20 x 20 feet. C, trees planted 24 x 24 feet. Note comparative size of the trees planted at 24 feet. BUL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES 19 Fig. 8. — Eight-year-old French prune trees. A, trees thinned several months before photographing from 12 x 12 feet to 24 x 24 feet. B ; trees originally planted 24 x 24 feet. Note the comparative size and vigor. 20 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION advantage. In planting- French prunes, he would consider setting' the trees 20 x 20 feet on the square with the idea of later removing the diagonal rows. Mr. E. A. Gammon, pear grower at Hood, believes peaches and plums might well be planted as temporary trees between pears set 18 x 18 feet under his conditions on the bottom lands of the Sacra- mento River. Fig. 9. — Twenty-year-old prune orchard interplanted with peaches. Peach trees, of which the one in the center foreground is the first of the row, are very weak, with little fruiting wood, while the prune trees in blossom on either side have not had proper chance for their best development. Batchelor 4 states, in connection with the practice of double planting walnuts 30 x 60 feet, that ' ' By this method properly carried out, nearly twice the tonnage may be expected during the first 10 to 14 years, as where only the permanent trees are planted." These instances are typical of the views of many orchardists. On the other hand, there are many growers who condemn the practice on the ground that the orchard will not be thinned in time and that the extra trees will not materially increase the returns. This opinion deserves special consideration with such fruits as the peach and the plum, which make a quick growth and come into bearing early. Double planting apple orchards does not seem feasible in the leading producing districts of California because there are no suitable 4 Batchelor, L. D. Walnut culture in California. Calif. Agr. Exp. Sta. Bui. 379:38. BUL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES 21 commercial varieties grown which will give profitable returns before the trees begin to crowd. Moreover, such fruits as plums or peaches, which might be suitable for this purpose, are not well adapted to the apple sections. Figure 10 shows a 14-year-old almond orchard where the trees are planted 30 x 30 feet apart quincunx system with peach fillers. Although the size of the trees has been reduced somewhat by crowding, good care and plenty of water have up to this time maintained sufficient Fig. 10. — Almond orchard with peach fillers. Almond trees 30 x 30 feet with peach trees in the center. vigor to make them profitable. Just how much longer they can continue to produce their present returns under such conditions is, however, difficult to state. The advisability and profitableness of the practice of double planting, therefore, depends primarily upon the kinds of fruit grown, the difference in time required for the permanent and temporary trees to reach good bearing age, the available water supply, and last, but perhaps most important of all, the courage of the grower to remove the temporary trees at the proper time. Thinning old orchards. — As mentioned previously, many of the older orchards, planted with little knowledge of how the trees would grow and at a time when very severe pruning was generally prac- ticed, are now badly crowded. Even with severe heading of the main limbs, often into two- and three-year-old wood, cultivation and spray- 22 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION ing has become difficult, and with the branches weighted down under a load of fruit, harvesting is much more of a task. How should such orchards be treated? Should they be allowed to remain as they are with the inconveniences and with the extra expense of handling, or should part of the trees be removed? The answer to these ques- tions depends almost entirely upon the individual orchard and upon the orchardist. In some cases, thinning would be recommended without hesitation. In others it would be considered a mistake, par- ticularly where thinning has been delayed until all the trees are permanently injured. With the peaches and apricots planted 12 x 12 feet apart on the University Farm, permanent injury occurred before any of the trees were removed, although to have thinned the trees much sooner would have meant removing them before any returns had been received. Figure, 1, showing the growth of apricots, peaches, and plums, discloses a slight gain in tree size in the plantings during the seasons of 1922 and 1923, but figures 6, 7, and 8 show that the trees were dwarfed, and in the case of the peach trees, were almost killed before thinning. A similar condition was observed in an old apple orchard in Sonoma County where the trees, long standing 20 x 20 feet, had been thinned several years previously to 40 x 40 feet. These trees, receiving only the natural rainfall, had competed with each other for soil moisture so long as to make any material increase in growth after thinning very doubtful. Moreover, 75 per cent of the trees had been removed so as to make a commercial crop practically impossible. The great majority of mistakes, however, have been those of not thinning ; a few specific instances of successful thinning are listed in table 4. In numerous instances in Orange County, very marked increases in walnut yields have been secured the third or fourth year after the removal of half the trees originally planted 40 feet apart. In considering the time and method of thinning, the system and distance of planting, severity of crowding, kind and age of trees, type of soil, and method of pruning should all be taken into consider- ation. The system and distance of planting determine the spacing and number of trees allowed to remain. While thinning to some extent may be done by removing only a few miscellaneous trees, even distribution can be secured only by taking out from 50 to 75 per cent of the original planting through the removal of alternate rows in one or both directions, either on the square or diagonal. The summary and diagrams in table 5 illustrate the different methods and the result of each. BUL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES 23 TABLE 4 Results of Orchard Thinning Fruit Planted Thinned Orchard When How When How Results E. A. Gammon, Hood Pears 1890 16 x 16 1915 22.5 x 32 Better trees and fruit and Wm. McKenzie, Monticello Prunes 1890 20x20 1917 28x28 larger yields. Larger and better fruit and Henry Wheatley, Napa Prunes 1900 18x18 1915 18x36 greater yields. Much larger trees. Com- parative yields, thinned and unthinned trees, 1925, the same, but more fruit of good size on thinned trees. H. G. Boyce, Winters Apricots 1893 24x24 1913 34x48 Trees using all the 34-foot H. G. Boyce, Winters Almonds 1883 24x24 1913 34x48 space. Large crops. Large crops. W. D. Wilkins, Mountain View. Apricots 1898 22x22 1910 22x44 Large trees with heavy yields. Limoneira Ranch, Santa Walnuts 1891 40x40 1916 40x80 No increase in yields for Paula. several years previous to thinning. Yields now doubled. TABLE 5 Systems of Thinning System of planting Method of thinning Reduc- tion in number of trees Form of planting after thinning Remarks Square 50% Rectangular Relieves crowding only in one direction. Alternate rows both direc- 75% Square Usually too severe. Too few tions. trees left. Alternate diagonal rows or 50% Quincunx Most common method. Re- alternate trees in each row. maining trees well spaced. 50% Square Trees quickly crowd in one direction. Quincunx Alternate rows or removal of tree in center of square. 50% Square planting to secure even dis- tribution. Hexagonal Alternate trees in alternate rows or tree in center of hexagon. 25% Hexagonal Thinning too light to be of great value. Hexagonal or Alternate tree in each row or 50% Irregular di- Relieves crowding only in one triangular. alternate diagonal rows. agonal. direction. Alternate rows either on the 75% Square or tri- Very satisfactory with large, square or diagonal and al- angular. thrifty, long-lived trees ternate tree in remaining which will satisfactorily row. utilize the space. With smaller, weaker trees, the thinning is too severe. 24 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION J: O J &—9 ■ T ° or o 3 O >t o >: o »t o J« (a) Removal of alternate rows. Square Planting (b) Removal of alternate rows in both directions. (c) Removal of alternate diagonal rows. Rectangular (d) Removal of alternate rows. (u) Removal of alternate diagonal rows. 6 % o o o o o o o o o o o - - - - 6 - ' - - < o o o --P 1-6 3 o o o o o o o o o o o Quincunx (e) Removal of alternate Hexagonal (f) Removal of alternate rows or the center tree of rows in either of two direc- tions. each square. S^ it f=^ <®JE 9 V 31 o Triangular (h) Removal of alternate (i) Removal of alternate rows and each even tree in rows and each odd tree in the remaining rows. the remaining rows. Fig. 11. — Systems of planting and methods of thinning. In figure 11 a uniform distance of 25 feet has been used as illustrative of the fact that although the systems of thinning have considerable similarity, they differ in the amount of space allowed each tree. Since it is often desirable to know the diagonal spacing between trees planted at different distances and according to the different systems, a few of these distances have been calculated. They are shown in table 6. BUL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES 25 TABLE <3 Diagonal Distances Between Trees Distances on the diagonal Distances of planting (1) Square planting (2) Alternate planting (3) Quincunx planting (4) Hexagonal planting (5) 18 x 18 25.5 20 1 20x20 28.3 22.4 22x22 31.1 24.6 25 x 25 35.3 27.9 27x27 38.2 30.2 One-half the distances given All trees equidistant. Same as 30 x 30 42 5 33.5 in column 2. column 1. 35 x 35 49.5 39.1 40x40 56.6 44.8 50x50 70.7 55.9 60 x 60 84.9 67 1 Where one has a choice of two methods, the one best adapted to the trees' needs should be chosen. If crowding and severe pruning has been necessary to keep the trees within bounds, the wider spacing should be chosen. If, on the other hand, the trees are on thin soil, have never been very vigorous, and have attained practically their full size, thinning should be done lightly. It is in this connection that the orchardist must rely upon his good judgment as to how many trees should be removed. An effort must be made to forecast the probable response of the trees to the thinning. As a rule this is not extremely difficult when the factors influencing the growth of the trees are considered. Vigorously growing trees with branches inter- lacing clearly need more room for their development. Mature or old bearing trees making little new wood growth each year may or may not respond to a wider spacing, depending upon the factors mentioned above. While such trees may have had their vigor checked by crowding, beneficial results from thinning can probably be secured only by encouraging more wood growth through a heavier pruning, an increased soil moisture supply, or perhaps by the addition of organic or nitrogenous fertilizers. In other words, crowding has been only one factor limiting their growth, and if better orchard manage- ment generally does not accompany thinning, removing a portion of the trees will only result in loss. While old trees may be rejuvenated after thinning, much better results can be expected by removing the crowding trees as soon as it is evident that such a condition exists. As pointed out in connection with double planting, thinning is usually delayed too long. For best results, it must be done before and not after the trees become weakened. This means that the grower must 26 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION have courage to cut out approximately half of his trees just at the time when they are in prime condition. Such a practice cannot but result in a financial loss for two or three years, but where thinning is justifiable, it will likewise result in a larger crop of better fruit during the future life of the orchard. It is to be decided, therefore, whether it is more desirable to secure the maximum returns over a relatively few years or have the yields gradually increase over a long period of time. In order to permit the removal of bearing trees with the least financial sacrifice, it is suggested that severe pruning be practiced on the trees which are to be removed for two or three seasons previous to thinning. This would allow for some crop returns and at the same time would permit expansion of the trees which are to remain. It should be pointed out in this connection, however, that the roots of the trees are still competing with each other for the moisture and plant food materials in the soil, and that unless these are present in large amounts, the yields will not be as good as when the entire tree is removed. Such a practice is only a temporary expedient. SUGGESTIONS FOR NEW PLANTINGS It should be evident that definite planting distances can be intelli- gently determined only by the individual grower who takes into con- sideration his soil, the habits of the fruit or variety in question, and the proposed method of handling his trees. However, the following suggestions, based upon results of the above experiments and the experience of the most successful growers, are offered as being of possible assistance to prospective planters. Almonds. — An extensive survey of the almond industry of the state by Mr. M. N. Wood of the United States Department of Agri- culture reveals the fact that planting distances vary from 16 to 35 feet, the majority of trees being set at an intermediate distance of approximately 25 feet. Few new orchards can be found where the trees are planted closer than 24 to 26 feet, and on the better types of soils where the trees are to have good care, and sufficient irrigation facilities, 30 feet is recommended. Exceptionally large individual trees have been found, one near Chico having a spread of branches of forty-seven feet. Apples. — Thirty by thirty feet has long been more or less of a standard planting distance in many apple sections of the United States. The majority of plantings in California, however, have been somewhat closer, although extreme crowding of the apple has not been so prevalent as has been the case with the other deciduous fruits. BUL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES 27 In most of the earlier plantings in the Watsonville district the trees were set 24 to 26 feet apart, while in the Sebastopol district most of the plantings are from 20 to 24 feet. These distances, especially for the leading variety, the Gravenstein, have proved too close. Except for small upright growing varieties, such as Eome Beauty, it is generally undesirable that the trees be planted closer than 30 feet apart. On the other hand, many varieties on good soil and under favorable conditions will easily utilize 35 feet with advantage. Partic- ularly is this true in coastal sections subject to fog where the trees and ripening fruit should be allowed the maximum sunlight obtainable. Apricots.— While many apricot orchards in the leading districts are planted with the trees at a distance of from 20 to 22 feet apart, newer plantings are made at a distance from 24 feet as a minimum to 35 feet as a maximum. On deep soil with plenty of water, 26 to 30 feet is recommended. The apricot generally is one of the larger growing fruit trees, and with a moderate system of pruning, most varieties, particularly the Moorpark, should be given plenty of room for development. Cherries. — Although sweet cherry trees are characterized by an upright habit of growth, they also attain large size under ideal conditions. Twenty-four feet is suggested as a minimum distance with from 26 to 30 feet as an optimum distance on fertile, moist, but well drained soils. As mentioned previously, individual trees have been noted in Sutter County which occupied 35 to 40 feet to advantage. Peaches. — Distances for planting peaches vary widely. In the peach sections of Placer County where many of the orchards are on comparatively shallow or thin soil, most of the present plantings are either 16 or 18 feet, and until more growth can be secured by additional water, fertility, or other means, it is doubtful if a distance greater than 20 feet is justifiable. In the producing sections of the San Joaquin and Sacramento valleys, many orchards, including the high yielding Brandstadt Orchard at Yuba City, are planted 20 feet apart. This distance, however, is believed even by the growers of that section to be too close for continued high yields. From 22 to 24 feet is regarded as more desirable. In many of the newer orchards now being planted, 24 feet is considered a minimum. Twenty-four to thirty feet is suggested by one of the leading nurserymen, and from the results of the experiments reported in this bulletin, the greater distance may frequently be used with advantage, even though bearing peach trees should be given a somewhat more severe pruning than the other deciduous fruits. 28 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Pears. — The pear tree seems peculiarly able to adapt itself to its environment. As pointed out, the trees in the experimental plots on the University Farm have maintained practically a healthy con- dition and fair vigor under the very close planting of 12 x 12 feet. Other trees in the same plots and also in other orchards have utilized a 30-foot spacing. Recommendations of from 25 to 30 feet are now quite common, but since moderate crowding at least does not seem detrimental, the 25-foot planting as a general maximum seems best for Bartletts. The majority of bearing orchards at present were planted between 20 and 24 feet. The trees are not large but do well at this distance. Pears in the Sierra foothills should naturally be planted closer than in the valley or river sections. Plums and prunes. — Since most varieties of shipping plums are of Japanese origin or hybrids of Prunus salicina stock, few make large trees, perhaps partly because of the inherent nature of the variety itself and partly because some of the leading plum sections do not have the deepest or most fertile soil. Eighteen to 20 feet is the distance usually accepted for planting in most districts. Some plant- ings in the Sierra foothills are as close as 16 feet, while the experiments under soil conditions at Davis indicate that 22 to 24 feet should be the minimum. The European or domestica type of plums, to which the prunes belong, produces a tree of considerably greater size and for the most part is grown commercially in sections favorable for good tree devel- opment. While a number of the older French prune orchards, particularly in Napa and Santa Clara Counties, were planted 18 and 20 feet apart, this distance can now be recommended only for very thin or poor soils. Some of the newer plantings are being set as far as 30 feet. Between these extremes, 22 to 26 feet is the most common average. On deep fertile soils 25 feet is suggested as a minimum distance. Walnuts. — Following the very beneficial results of the walnut growers of Orange County in thinning their groves, 60 feet is the distance most frequently recommended at which trees should stand after about 10 to 12 years. The majority, however, favor double planting either 30 x 60 or 60 x 60 quincunx system and removing the surplus trees when they begin to crowd. In some of the non-irrigated sections of northern California where the trees do not attain such large size, 45 to 50 feet is felt to be the most profitable distance for the permanent trees. Almonds or peaches are frequently used as fillers during the first eight or ten years of the life of the orchard. BUL. 414] PLANTING DISTANCES FOR DECIDUOUS FRUIT TREES 29 SUMMARY Close planting for the fruit or variety concerned is recommended (a) where the trees naturally fail to attain large size; (b) where small trees are desired and heavy pruning is practiced annually ; and (c) where it is the desire to secure the greatest returns from the orchard during the first few crop years rather than the maximum average returns over a considerably longer period. Close planting with the idea of thinning out a portion of the trees is aptly summed up by one grower who states, "All is well with close planting, if the trees are thinned before the branches and root systems begin to compete for space, but observation tells you most growers delay this far too long. ' ' The desirability of relatively wide planting is becoming more clearly recognized with almost all deciduous fruits grown under favorable soil and moisture conditions and under a moderate system of pruning. While something is sacrificed in the size of the first few crops, the yields tend to increase steadily, the orchard continues to produce better quality and more consistent yields over a greater length of time. ACKNOWLEDGMENTS The writer herewith wishes to express his appreciation to Messrs. M. W. Dula, Robt. M. Peckham, and Henry Sevier, past and present Orchardists, and to Mr. Lloyd Austin, former Assistant in Pomology, for assistance in securing growth measurements and yield data annually ; to Miss Edna Russ for assistance in the keeping of records and for photographic work. Much gratitude is due numerous fruit growers interviewed and to Farm Advisors and Horticultural Com- missioners, who willingly gave of their time in connection with this study. STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION No. 253. Irrigation and Soil Conditions in the Sierra Nevada Foothills, California. 261. Melaxuma of the Walnut, "Juglans regia." 262. Citrus Diseases of Florida and Cuba Compared with Those of California. 263. Size Grades for Ripe Olives. 268. Growing and Grafting Olive Seedlings. 273. Preliminary Report on Kearney Vine- yard Experimental Drain. 275. The Cultivation of Belladonna in California. 276. The Pomegranate. 277. Sudan Grass. 278. Grain Sorghums. 279. Irrigation of Rice in California. 283. The Olive Insects of California. 294. Bean Culture in California. 304. A Study of the Effects of Freezes on Citrus in California. 310. Plum Pollination. 312. Mariout Barley. 313. Pruning Young Deciduous Fruit Trees. 319. Caprifigs and Caprification. 324. Storage of Perishable Fruit at Freez- ing Temperatures. 325. Rice Irrigation Measurements and Experiments in Sacramento Valley, 1914-1919. 328. Prune Growing in California. 331. Phylloxera-Resistant Stocks. 335. Cocoanut Meal as a Feed for Dairy Cows and Other Livestock. 339. The Relative Cost of Making Logs from Small and Large Timber. 340. Control of the Pocket Gopher in California. 343. Cheese Pests and Their Control. 344. Cold Storage as an Aid to the Mar- keting of Plums. 346. Almond Pollination. 347. The Control of Red Spiders in Decid- uous Orchards. 348. Pruning Young Olive Trees. 349. A Study of Sidedraft and Tractor Hitches. 350. Agriculture in Cut-over Redwood Lands. 352. Further Experiments in Plum Pollina- tion. 353. Bovine Infectious Abortion. 354. Results of Rice Experiments in 1922. 357. A Self-mixing Dusting Machine for Applying Dry Insecticides and Fungicides. 358. Black Measles, Water Berries, and Related Vine Troubles. 361. Preliminary Yield Tables for Second Growth Redwood. 362. Dust and the Tractor Engine. 363. The Pruning of Citrus Trees in Cali- fornia. 364. Fungicidal Dusts for the Control of Bunt. 365. Avocado Culture in California. 366. Turkish Tobacco Culture, Curing and Marketing. 367. Methods of Harvesting and Irrigation in Relation of Mouldy Walnuts. 368. Bacterial Decomposition of Olives dur- ing Pickling. 369. Comparison of Woods for Butter Boxes. BULLETINS No. 370. 371. 372. 373. 374. 376. 377. 379. 380. 381. 382. 383. 385. 386. 387. 388. 389. 390. 391. 392. 393. 394. 395. 396. 397. 398. 399. 400. 401. 402. 403. 404. 405. 406. 407. 408. 409. 410. 411. 413. 414, Browning ot Yellow Newtown Apples. The Relative Cost of Yarding Small and Large Timber. The Cost of Producing Market Milk and Butterfat on 246 California Dairies. Pear Pollination. A Survey of Orchard Practices in the Citrus Industry of Southern Cali- fornia. Results of Rice Experiments at Cor- tena, 1923. Sun-Drying and Dehydration of Wal- nuts. The Cold Storage of Pears. Walnut Culture in California. Growth of Eucalyptus in California Plantations. Growing and Handling Asparagus Crowns. Pumping for Drainage in the San Joaquin Valley, California. Monilia Blossom Blight (Brown Rot) of Apricot. Pollination of the Sweet Cherry. Pruning Bearing Deciduous Fruit Trees. Fig Smut. The Principles and Practice of Sun- drying Fruit. Berseem or Egyptian Clover. Harvesting and Packing Grapes in California. Machines for Coating Seed Wheat with Copper Carbonate Dust. Fruit Juice Concentrates. Crop Sequences at Davis. Cereal Hay Production in California. Feeding Trials with Cereal Hay. Bark Diseases of Citrus Trees. The Mat Bean (Phaseolus aeonitifo- lius). Manufacture of Roquefort Type Cheese from Goat's Milk. Orchard Heating in California. The Blackberry Mite, the Cause of Redberry Disease of the Himalaya Blackberry, and its Control. The Utilization of Surplus Plums. Cost of Work Horses on California Farms. The Codling Moth in Walnuts. Farm-Accounting Associations. The Dehydration of Prunes. Citrus Culture in Central California. Stationary Spray Plants in California. Yield, Stand and Volume Tables for White Fir in the California Pine Region. Alternaria Rot of Lemons. The Digestibility of Certain Fruit By- products as Determined for Rumi- nants. Factors Affecting the Quality of Fresh Asparagus after it is Harvested. Paradichlorobenzene as a Soil Fumi- gant. A Study of the Relative Values of Cer- tain Root Crops and Salmon Oil as Sources of Vitamin A for Poultry. The California Poultry Industry; a Statistical Study. Planting and Thinning Distances for Deciduous Fruit Trees. No. 87. 117. 127. 129. 136. 144. 157. 160. 164. 166. 170. 173. 178. 179. 190. 199. 202. 203. 209. 210. 212. 215. 217. 220. 228. 230. 231. 232. 234. 235. 236. 237. 238. 239. 240. 241. 243. 244. 245. 247. 248. 249. 250. 252. 253. 254. Alfalfa. The Selection and Cost of a Small Pumping Plant. House Fumigation. The Control of Citrus Insects. Melilotus indica as a Green-Manure Crop for California. Oidium or Powdery Mildew of the Vine. Control of the Pear Scab. Lettuce Growing in California. Smali Fruit Culture in California. The County Farm Bureau. Fertilizing California Soils for the 1918 Crop. The Construction of the Wood-Hoop Silo. The Packing of Apples in California. Factors of Importance in Producing Milk of Low Bacterial Count. Agriculture Clubs in California. Onion Growing in California. County Organizations for Rural Fire Control. Peat as a Manure Substitute. The Function of the Farm Bureau. Suggestions to the Settler in California. Salvaging Rain-Damaged Prunes. Feeding Dairy Cows in California. Methods for Marketing Vegetables in California. Unfermented Fruit Juices. Vineyard Irrigation in Arid Climates. Testing Milk, Cream, and Skim Milk for Butterfat. The Home Vineyard. Harvesting and Handling California Cherries for Eastern Shipment. Winter Injury to Young Walnut Trees during 1921-22. Soil Analysis and Soil and Plant Inter-relations. The Common Hawks and Owls of California from the Standpoint of the Rancher. Directions for the Tanning and Dress- ing of Furs. The Apricot in California. Harvesting and Handling Apricots and Plums for Eastern Shipment. Harvesting and Handling Pears for Eastern Shipment. Harvesting and Handling Peaches for Eastern Shipment. Marmalade Juice and Jelly Juice from Citrus Fruits. Central Wire Bracing for Fruit Trees. Vine Pruning Systems. Colonization and Rural Development. Some Common Errors in Vine Prun- ing and Their Remedies. Replacing Missing Vines. Measurement of Irrigation Water on the Farm. Supports for Vines. Vineyard Plans. The Use of Artificial Light to Increase Winter Egg Production. CIRCULARS No. 255. 256. 257. 258. 259. 261. 262. 263. 264. 265. 266. 269. 270. 272. 273. 274. 276. 277. 278. 279. 281. 282. 283. 284. 285. 286. 287. 288. 289. 290. 291. 292. 293. 294. 295. 298. 299. 300. 301. 302. 303. 304. 305. 306. 307. 308. Leguminous Plants as Organic Fertil- izer in California Agriculture. The Control of Wild Morning Glory. The Small-Seeded Horse Bean. Thinning Deciduous Fruits. Pear By-products. Sewing Grain Sacks. Cabbage Growing in California. Tomato Production in California. Preliminary Essentials to Bovine Tuberculosis Control. Plant Disease and Pest Control. Analyzing the Citrus Orchard by Means of Simple Tree Records. The Tendency of Tractors to Rise in Front; Causes and Remedies. An Orchard Brush Burner. A Farm Septic Tank. California Farm Tenancy and Methods of Leasing. Saving the Gophered Citrus Tree. Fusarium Wilt of Tomato and its Con- trol by Means of Resistant Varieties. Home Canning. Head, Cane, and Cordon Pruning of Vines. Olive Pickling in Mediterranean Coun- tries. The Preparation and Refining of Olive Oil in Southern Europe. The Results of a Survey to Determine the Cost of Producing Beef in Cali- fornia. Prevention of Insect Attack on Stored Grain. Fertilizing Citrus Trees in California. The Almond in California. Sweet Potato Production in California. Milk Houses for California Dairies. Potato Production in California. Phylloxera Resistant Vineyards. Oak Fungus in Orchard Trees. The Tangier Pea. Blackhead and Other Causes of Loss of Turkeys in California. Alkali Soils. The Basis of Grape Standardization. Propagation of Deciduous Fruits. The Growing and Handling of Head Lettuce in California. Control of the California Ground Squirrel. The Possibilities and Limitations of Cooperative Marketing. Poultry Breeding Records. Coccidiosis of Chickens. Buckeye Poisoning of the Honey Bee. The Sugar Beet in California. A Promising Remedy for Black Measles of the Vine. Drainage on the Farm. Liming the Soil. A General Purpose Soil Auger and its Use on the Farm. American Foulbrood and its Control. Cantaloupe Production in California. The publications listed above may be had by addressing College of Agriculture, University of California, Berkeley, California. 12m-ll,'26