UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 THE EFFECT OF PRUNING IN THE 
 TRAINING OF YOUNG OLIVE TREES 
 
 H.E.JACOB 
 
 BULLETIN 568 
 
 JANUARY, 1934 
 
 UNIVERSITY OF CALIFORNIA 
 BERKELEY, CALIFORNIA 
 
Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of California, Davis Libraries 
 
 http://www.archive.org/details/effectofpruningi568jaco 
 
THE EFFECT OF PRUNING IN THE 
 TRAINING OF YOUNG OLIVE TREES 1 
 
 H. E. JACOBS 
 
 The investigation reported in this paper constitutes a continuation 
 and an expansion of the investigation reported by Bioletti 3 in Bulletin 
 348. The results of the former investigation show a very decided depress- 
 ing effect on young olive trees resulting apparently from both very 
 heavy and moderately heavy pruning. Trees which had received four 
 successive severe winter prunings made only one-tenth as much average 
 growth as was made by the unpruned trees. Those which had received 
 two light summer prunings and two heavy winter prunings made only 
 one-fourth the average growth of the unpruned trees. Furthermore the 
 unpruned trees were the first to come into bearing and their form was 
 equal to or better than that of the pruned trees. These results suggested 
 the idea that at least the Mission and probably all varieties of olive trees 
 would develop faster, bear earlier, and possibly attain a better form if 
 left unpruned, or practically so, until they reached bearing age. 
 
 Certain difficulties were encountered in carrying out the former in- 
 vestigation. In one part of the plot the trees did not receive sufficient 
 water owing to a shortage of irrigation water at the time it was needed. 
 Here the depressing effect of severe pruning was less evident probably 
 because the unpruned trees sooner felt the limiting effect of restriction 
 in water supply. In the part receiving sufficient water, the effect of com- 
 petition between the pruned and unpruned was evident after the fourth 
 season. The unpruned trees developed most rapidly, monopolized more 
 than their share of soil, and shaded the smaller pruned trees during 
 parts of each day. Consequently the pruned trees suffered not only from 
 the depressing effect of the pruning but from competition with their 
 vigorous rivals — the unpruned trees — for water, light, and soil nutri- 
 ents. It seemed advisable therefore to repeat the experiment in a modi- 
 fied form and also to extend the work to varieties other than the Mission, 
 which alone was used in the original experiment. 
 
 i Eeceived for publication August 11, 1933. 
 2 Associate in Viticulture. 
 
 s Bioletti, F. T. Pruning young olive trees. California Agr. Exp. Sta. Bui. 348 : 
 87-110. Figs. 1-8. 1922. 
 
 [3] 
 
4 University of California — Experiment Station 
 
 A new experimental plot was planted in 1924. The trees of this plot 
 have reached bearing age and the phase of the investigation dealing with 
 the pruning of young trees has been completed. The plan of the experi- 
 ment and the results obtained are given in the following pages. 
 
 Fig. 1. — Mission tree 5 years old having had no pruning. Illustrates 
 system A before pruning in 1929. 
 
 VARIETIES USED 
 
 Mission, Manzanillo, Sevillano, and Ascolano — the four varieties of 
 olives of most importance in California — were used. The Mission tree is 
 of upright growth and very vigorous (fig. 1 ) . The Manzanillo is drooping 
 and less vigorous (fig. 11). The Sevillano and Ascolano are nearly as 
 vigorous as the Mission and intermediate between the Mission and Man- 
 zanillo in habit of growth (fig. 4) . 
 
Bul. 568J 
 
 Effect of Pruning Young Olive Trees 
 
 PRUNING SYSTEMS USED 
 
 Variations in pruning were confined to winter pruning. Summer prun- 
 ing was limited to the removal of shoots from the rootstocks and of 
 water-sprouts on the trunks. No summer pruning was done in the tops 
 of any of the trees. Five systems of winter pruning were employed. 
 
 Fig. 2. — Mission tree 5 years old shaped by a single pruning. The 
 tree has been opened up by removing several large branches and 
 lightly thinning out the laterals on the remaining branches. Illus- 
 trates system A after pruning in 1929. Same tree as in figure 1. 
 
 System A : Under this system little or no pruning of the branches was 
 practiced until the trees reached bearing age. During the first five years 
 an occasional ill-placed branch was removed where it seemed evident 
 that its removal later would damage other branches needed to form the 
 
6 University of California — Experiment Station 
 
 permanent framework of the tree. Suckers or water-sprouts at or below 
 the surface of the soil were removed several times each year during the 
 first three years. No thinning of twigs or small branches was done on any 
 part of the tree during the first four years. 
 
 Fig. 3. — Mission tree 5 years old which has been shaped by light 
 annual priming. Illustrates system C after pruning in 1929. 
 
 A light crop was borne the fifth season. The following winter the trees 
 were opened up by removing all of the main branches except four, five, 
 or six scaffold branches on each tree. These reserved branches were 
 selected so as to form as nearly as possible a hollow inverted cone with 
 sides rising at an angle of about 60 degrees from the horizontal. After 
 the removal of superfluous large branches, the lower half of the tree was 
 thinned out by the removal of twigs or by cutting back to laterals as 
 much as appeared necessary to prevent overbearing. No topping of the 
 main branches was done. (See figs. 1 and 2, 4 and 5, 11 and 12.) 
 
Bul. 568 
 
 Effect of Pruning Young Olive Trees 
 
 During' the sixth and seventh winters the pruning consisted in the re- 
 moval of water-sprouts and light thinning of dense portions of the trees. 
 
 System, B : This system is identical with system A except that the very 
 dense skirt of small branches on the lower part of the tree was thinned 
 out the third winter. 
 
 Fig. 4. — Ascolano tree 5 years old having had no pruning. 
 Illustrates system A before pruning in 1929. 
 
 System C: This may be designated as light annual pruning. At the 
 first or second winter pruning, from three to five branches were selected 
 for scaffold branches from which the framework of the tree was devel- 
 oped (fig. 3) . These were selected so as to be well distributed around the 
 trunk and with their respective origins from the trunk as far apart 
 vertically as the development of the individual tree would permit. 
 
 Each year branches not desired for the scaffold were repressed by 
 shortening, or were removed entirely where their presence threatened 
 to interfere seriously with the development of the desired form. Surplus 
 
8 University of California — Experiment Station 
 
 branches were allowed to remain wherever this was possible without 
 seriously affecting the development of the scaffold branches. To obtain 
 an even development of the permanent branches, the few that grew much 
 more vigorously than the others were restrained by cutting back to a 
 lateral extending in the desired direction. 
 
 Fig. 5. — The same Ascolano tree as shown in figure 4, after 
 pruning. Illustrates system A after pruning in 1929. 
 
 The skirt of small branches on the lower part of the tree was thinned 
 out lightly at each annual pruning. The growth on the scaffold branches 
 of the Manzanillo was thinned out annually in order to lighten the 
 weight of crop and foliage and reduce the tendency to droop. This was 
 done also with Sevillano and Ascolano in cases where they showed the 
 same tendency. The thinning was done by removing laterals or portions 
 of laterals. No thinning was done on the scaffold branches of the Mission 
 until the fifth winter. 
 
 At the fifth winter pruning, most of the surplus branches which had 
 
Bul. 568] 
 
 Effect of Pruning Young Olive Trees 
 
 been held back by annual pruning were removed entirely and the growth 
 on the scaffold branches, where very dense, was thinned out to prevent 
 overbearing the following season. This thinning out of laterals on the 
 scaffold branches was fairly heavy with the Manzanillo, Sevillano, and 
 Ascolano, and very light with the Mission (figs. 3 and 6) . 
 
 *}i.w. 
 
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 5 .* 
 
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 Pig. 6. — Ascolano tree 5 years old which has been shaped by light 
 annual pruning. Illustrates system C after pruning in 1929. 
 
 System D : The pruning under this system was identical with that of 
 system C, but in addition to pruning, mechanical means were employed 
 where needed to hold the scaffold branches in position for one or two 
 seasons. On the Mission a double-pointed piece of hardwood was inserted 
 between crowding scaffold branches to hold them apart for one season, 
 after which they maintained their relative positions without the 
 spreader. Not more than three spreaders were used on any tree and most 
 of the trees did not require any. 
 
 With the Manzanillo trees under this system the scaffold branches 
 
10 
 
 University of California — Experiment Station 
 
 were supported during the second and third seasons by bands of burlap 
 about 3 inches wide passed around the tree and nailed to a stake about 
 4 l / 2 feet high (figs. 7 and 13). Where individual scaffold branches 
 showed a strong tendency to droop and could not be supported by this 
 means, owing to the limited height of the stake, they were supported by 
 
 Fig. 7. — Manzanillo tree 2 years old supported by 
 ;i l>and of cloth passed around the tree and the ends 
 nailed to a stake. 
 
 tying to one or two opposing branches by means of tarred grape twine. 
 The twine was fastened to screw-eyes inserted in the respective branches. 
 Many branches were supported in this manner during the third season 
 and a few during the fourth season. No tying was done after the fourth 
 season. 
 
 The scaffold branches of the Sevillano and Ascolano grew very nearly 
 in the desired position and required practically no artificial support. An 
 occasional branch was kept in place with tarred grape twine and screw- 
 eyes as was done with the Manzanillo. 
 
Bul. 5(38" 
 
 Effect of Pruning Young Olive Trees 
 
 11 
 
 System, E : The trees under this system were heavily pruned annually. 
 At the first winter pruning three or four branches were selected for 
 scaffold branches and all others removed. These selected branches were 
 cut back to about 6 inches and all of their lateral branches removed. At 
 the second and subsequent primings, all new branches and twigs starting 
 
 
 
 
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 Fig. 8. — Ascolano tree 5 years old which has been severely pruned annually. 
 Left, before pruning in 1929. Eight, the same tree after pruning in 1929. 
 
 from the trunk were removed and the growth on the scaffold branches 
 was heavily thinned. Any scaffold branch not growing in the desired 
 direction was cut back to a lateral extending in the proper direction and 
 the other branches were cut back to a similar height. This type of pruning 
 was continued for five successive seasons. It was intended to be as nearly 
 as possible a duplication of the heavy annual pruning practiced in the 
 previous experiment and reported in Bulletin 348, but on a different 
 variety — Ascolano (fig. 8) . Mission was used in the former investigation. 
 
12 
 
 University of California — Experiment Station- 
 
 spacing AND ARRANGEMENT OF THE TREES 
 
 An orchard of 168 trees was planted in March, 1924, at the University 
 Farm, Davis, in accordance with the planting plan shown in figure 9. 
 
 A permanent orchard of trees spaced 30 x 30 feet was desired for 
 future experiments in pruning bearing trees. In order, however, to pro- 
 
 N 
 W E 
 
 S Irrig 
 
 line 
 
 Pruning 
 
 system Row 1 2 
 
 1 
 2 
 3 
 4 
 
 5 
 6 
 7 
 
 8 
 
 9 
 
 10 
 11 
 12 
 13 
 14 
 15 
 16 
 17 
 
 ORCHARD PLAN 
 
 Trees in the row 
 
 1 2 • 
 
 ' 
 • 
 o • 
 o • 
 
 • 
 • 
 
 o • 
 
 ' 
 
 3 4 
 
 
 
 
 
 
 
 
 
 
 
 
 5 6 
 
 
 
 
 
 
 
 
 
 
 7 8 
 
 
 
 
 
 
 
 
 
 
 
 - permanent trees 
 . - temporary trees 
 
 9 10 11 12 
 
 Fig. 9. — Planting plan of the pruning plot. 
 
 vide a larger number of young trees upon which to try the various sys- 
 tems of pruning young trees, half of the area of the plot was planted 
 15 x 15 feet and the other half 30 x 30 feet; three-fourths of the close- 
 planted trees were to be removed when they reached bearing age. This 
 spacing was sufficient to allow uniform development of the individual 
 trees up to bearing age, and all the trees of the orchard were therefore 
 used in the tests. The plot was bordered on all four sides by avenues or 
 roadways 20 feet or more in width. 
 
Bul. 5(38] Effect of Pruning Young Olive Trees 13 
 
 PLANTING 
 
 The Mission trees were grown from cuttings in a nursery at Davis. At 
 the time of planting in the orchard they were several years old and the 
 circumference of the trunks (measured 4 inches above the ground level) 
 varied from 8.4 inches for the largest to 5.5 inches for the smallest (see 
 table 1). 
 
 The Manzanillo, Sevillano, and Ascolano trees were purchased from 
 commercial nurseries. All were grafted on Redding 4 stock and their 
 exact age was unknown. At 4 inches above the ground level the Man- 
 zanillo trees varied in trunk circumference from 1.9 to 1.1 inches; the 
 Sevillano from 1.7 to 1.1 inches; and the Ascolano from 2.1 to 1.1 inches. 
 
 Pruning before planting consisted, in the case of the Mission, in 
 removing all except two or three of the largest branches — removing all 
 laterals and foliage from the retained branches, and shortening them to 
 about 4 inches. The trunk was cut back to not over 30 inches from the 
 ground level. All branches and leaves were removed from the trunks of 
 the Manzanillo, Sevillano, and Ascolano trees, and the trunks were cut 
 back to within 24 inches of the ground level. 
 
 The trees were graded before planting according to circumference of 
 trunk, the measurements being taken at the ground level of the nursery 
 row. 
 
 In planting, the trees were arranged according to size in order to 
 avoid competition between small and large trees. For example in the case 
 of the Mission, beginning with the largest tree and progressively using 
 trees of smaller size, the order of planting was as follows : Row 1, tree 1; 
 row 2, tree 1; row 3, tree 1; row 4, tree 1; row 4, tree 2; row 3, tree 2; 
 row 2, tree 2; row 1, tree 2; row 1, tree 3, etc. After planting, the trees 
 were whitewashed and were given a light irrigation. 
 
 For permanent record, circumference measurements were made after 
 planting, at a height of approximately 4 inches above the soil level 
 (table 1). 
 
 CULTURAL CONDITIONS 
 
 The soil of the plot belongs to the Yolo loam series and, to a depth 
 of 4 feet, is without marked variations in texture over the area of the 
 plot. Before planting, the land had been subsoiled 18 inches deep at 
 intervals of 3 feet and fallowed for one season. It had been in annual 
 crops for some years and was well leveled for irrigation. 
 
 4 A strong-growing variety often misnamed Picholine. 
 
14 
 
 University of California — Experiment Station 
 
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Bul. 568] Effect of Pruning Young Olive Trees 15 
 
 The planting, subsequent cultivation, and irrigation were carried out 
 uniformly with all plots. No defect in cultural care was noted except 
 that in October, 1931, the fruit of several of the close-planted trees 
 shriveled owing to insufficient soil moisture. 
 
 At the end of the first growing season several trees were dead and a 
 few more had grown poorly. All dead and weak trees were replaced in 
 the spring of 1925 with good trees of similar size and of the same variety. 
 The number of replaced trees was : Mission, 0; Sevillano, 7; Ascolano, 7; 
 Manzanillo, 5. Their position in the plot is shown by italics in table 1. 
 
 DATA COLLECTED 
 Annual measurements and records were made for each tree, showing : 
 
 1. Circumference of the trunk, measured by means of a steel tape 
 passed around the trunk at a height of approximately 4 inches from the 
 ground level. The trunk circumferences were then converted to trunk 
 cross-section areas (table 4 and fig. 10). 
 
 2. Weights of primings (table 2). 
 
 3. Estimated fraction (percentage) of the total foliage removed by 
 pruning during each of the first three years (table 3) . 
 
 4. Height of the tree — the average height of an imaginary line drawn 
 across the two highest points of the tree (table 5) . 
 
 5. Spread of the tree — the greatest distance in an east and west direc- 
 tion, between imaginary lines forming opposite sides of the general 
 contour of the individual tree (table 5) . 
 
 6. Weights of crops (table 6) . 
 
 7. Character of the crop as to graded sizes (table 6) . 
 
 DISCUSSION OF THE DATA 
 
 The measurements 'of tree and crop indicate the specific influence of 
 pruning and the relative merits of the several systems of training when 
 applied to the four varieties. The results are summarized in tables 1 to 6. 
 
 Weights of Primings. — The individual weights of the primings of 
 each tree have been averaged for each row and year (table 2). The 
 figures include the prunings from all trees — original plantings and 
 replants. Since the pruning was done in February or March of each year 
 the first winter pruning was in 1925, the second in 1926, and so on. The 
 trees developed slowly and unevenly during the first two years. The 
 pruning during these years was in accordance with the plan except that 
 any trees of the C and D systems which had made an insufficient growth 
 
16 
 
 University of California — Experiment Station 
 
 for the selection of scaffold branches were left unpruned until the second 
 winter (1926). 
 
 There are no consistent differences in the total weight of primings 
 taken with the systems A, B, C, and D during the first 6 years. With 
 system E the total weight of primings exceeded the average for the 
 variety (Ascolano) in the other sj^stems by 53 per cent (table 2). 
 
 TABLE 2 
 Average Weight Per Tree of Prunings Removed Each Year, in Pounds 
 
 Variety 
 
 Mission 
 
 Sevillano 
 
 Ascolano 
 
 Manzanillo. 
 
 Row 
 
 Pruning 
 system 
 
 1925* 
 
 26 
 24 
 
 00 
 02 
 
 04 
 02 
 02 
 
 07 
 07 
 
 1926 
 
 3 9 
 1 7 
 8 
 
 6 
 
 7 
 
 1927 
 
 29.0 
 11 4 
 15.0 
 
 7.5 
 3 1 
 2.9 
 
 9 5 
 9 2 
 2 6 
 1 5 
 
 5 5 
 
 11 
 1.5 
 
 1928 
 
 15 4 
 16.5 
 
 10.1 
 11 2 
 
 17 1 
 10.6 
 10.6 
 
 6.6 
 4.8 
 
 1929 
 
 87.1 
 47.7 
 
 12 1 
 17.8 
 
 37.2 
 21.8 
 16 3 
 13.6 
 
 43 8 
 26.4 
 29.7 
 
 13 
 15.6 
 
 9.2 
 19.6 
 11.2 
 
 1930 
 
 9.0 
 13.6 
 27.7 
 30.4 
 
 14 .3 
 12 3 
 24.2 
 20.5 
 
 16.9 
 12 3 
 16 5 
 16 1 
 19 4 
 
 4 
 3.7 
 17.4 
 11 4 
 
 Total of 
 six years 
 
 u<) 
 
 * The pruning was done in February or March of the year indicated. 
 
 The percentage of the foliage removed from each tree by pruning was 
 carefully estimated for the first three prunings. At the fourth and sub- 
 sequent prunings the trees were so large that such estimates were very 
 difficult to make and they were discontinued. Table 3 gives the average 
 estimated percentage of foliage removed from the trees of each row for 
 each of the first three seasons. 
 
 In April, 1931, all of the trees of rows 1 and 3, and trees 1, 3, 5, and 7 
 of rows 2 and 4 were removed and weighed in order to make direct com- 
 parison of the amount of growth made by the annually pruned trees of 
 systems C and D with that made by the trees of systems A and B which 
 had not been pruned each year. The trees were first cut off at a con- 
 venient height, and weighed. The stumps were then pulled and the roots 
 cut off close to the base of the trunk. The trunks were weighed and their 
 weights added to the respective top weights. No attempt was made to 
 
Bul. 568 
 
 Effect of Pruning Young Olive Trees 
 
 17 
 
 obtain the weight of the roots. To the weight of each tree was added the 
 total weight of primings removed from it during the previous years. 
 
 The mean weight of the total growth — weight of the tree plus all 
 previous prunings — of the annually pruned trees (systems C and D) 
 was 454.9 zb 36.8 pounds; while that of the trees not annually pruned 
 (systems A and B) was 519.1 ± 21.2 pounds. The difference is not 
 
 TABLE 3 
 
 Average Estimated Percentage of the Foliage Kemoved by Pruning 
 
 Variety 
 
 Row 
 
 Pruning 
 system 
 
 1925 
 
 1926 
 
 1927 
 
 f 
 
 1 
 
 A 
 
 
 
 
 1 
 Mission <, 
 
 o 
 3 
 
 B 
 
 C 
 
 7 
 
 5 
 
 34 
 14 
 
 1 
 
 4 
 
 D 
 
 6 
 
 7 
 
 19 
 
 f 
 
 5 
 
 A 
 
 
 
 
 
 
 6 
 
 7 
 
 B 
 C 
 
 
 
 24 
 
 22 
 
 
 
 13 
 
 1 
 
 8 
 
 I) 
 
 8 
 
 34 
 
 12 
 
 
 
 9 
 
 A 
 
 
 
 
 
 
 10 
 
 B 
 
 
 
 28 
 
 Ascolano ■ 
 
 
 11 
 
 E 
 
 34 
 
 70 
 
 70 
 
 
 
 12 
 
 D 
 
 3 
 
 35 
 
 16 
 
 
 
 13 
 
 C 
 
 3 
 
 19 
 
 6 
 
 
 14 
 
 B 
 
 
 
 35 
 
 
 
 15 
 
 16 
 
 A 
 D 
 
 20 
 
 20 
 
 
 
 12 
 
 
 17 
 
 c 
 
 25 
 
 32 
 
 15 
 
 significant and it appears that the trees under the two general types of 
 pruning made approximately equal total growth over the period of the 
 experiment (7 years) . 
 
 Cross-Section Areas of Trunks. — The individual trunk circumference 
 measurements were converted to cross-section areas and have been aver- 
 aged for each row and each year as shown in table 4. They are sum- 
 marized graphically in figure 10. 
 
 The unpruned trees (system A, rows 1, 5, 9, and 15) were difficult to 
 measure because of branches very close to the ground. It is probable that 
 the measurements recorded for these trees are slightly greater than the 
 actual circumferences. The figures indicate that the unpruned trees in 
 rows 1, 5, and 9 of the Mission, Sevillano, and Ascolano varieties, respec- 
 tively, made appreciably greater growth prior to 1929 than was made 
 by the trees of these varieties under any of the other pruning systems. 
 
18 
 
 University of California — Experiment Station 
 
 After the severe thinning out of the branches of these trees in 1929, the 
 differences decreased and almost disappeared by 1931 (fig. 10) . 
 
 With the Manzanillo trees the case is reversed. The trees unpruned 
 up to 1929, and those lightly pruned only once prior to 1929 (systems 
 A and B, rows 15 and 14). made less growth than the annually pruned 
 
 TABLE 4 
 
 Average Trunk Cross-Section Area of the Trees of Each Row by Years, 
 in Square Inches* 
 
 Variety 
 
 Row 
 
 Pruning 
 system 
 
 1924f 
 
 1925 
 
 1926 
 
 1927 
 
 1928 
 
 1929 
 
 1930 
 
 1931 
 
 
 ' 
 
 1 
 
 A 
 
 3 83 
 
 3.88 
 
 6 68 
 
 14 2S 
 
 27.90 
 
 37.98 
 
 53 17 
 
 Trees 
 removed 
 
 Mission ' 
 
 
 2 
 
 B 
 
 3 46 
 
 3.57 
 
 5.81 
 
 13.72 
 
 22.37 
 
 33.08 
 
 47.66 
 
 72.17J 
 
 
 3 
 
 C 
 
 3 75 
 
 3.77 
 
 4.87 
 
 11 55 
 
 21 10 
 
 27.59 
 
 40.58 
 
 Trees 
 
 
 
 
 
 
 
 
 
 
 
 
 removed 
 
 
 
 4 
 
 D 
 
 3 32 
 
 3 53 
 
 5 53 
 
 13 83 
 
 24.26 
 
 33.68 
 
 50.50 
 
 78.74 
 
 f 
 
 5 
 
 A 
 
 0.16 
 
 28 
 
 2.08 
 
 10 23 
 
 23.25 
 
 32.46 
 
 45 01 
 
 51.31 
 
 Sevillano { 
 
 6 
 
 B 
 
 14 
 
 25 
 
 1.81 
 
 7 44 
 
 18.12 
 
 22 41 
 
 38.47 
 
 49.89 
 
 7 
 
 c 
 
 0.16 
 
 26 
 
 1.58 
 
 6.40 
 
 16.62 
 
 23 45 
 
 36.52 
 
 48 65 
 
 K 
 
 8 
 
 D 
 
 14 
 
 26 
 
 1 46 
 
 5.66 
 
 13.98 
 
 23.00 
 
 34 04 
 
 46.73 
 
 ( 
 
 9 
 
 A 
 
 0.19 
 
 31 
 
 1 83 
 
 7 11 
 
 18.85 
 
 26 57 
 
 35 73 
 
 50.90 
 
 i 
 
 10 
 
 B 
 
 0.17 
 
 0.31 
 
 1 55 
 
 5 21 
 
 12 40 
 
 20.82 
 
 36 49 
 
 49.63 
 
 Ascolano i 
 
 11 
 
 E 
 
 19 
 
 0.28 
 
 0.88 
 
 4.17 
 
 9 16 
 
 13.30 
 
 18 26 
 
 24.54 
 
 1 
 
 12 
 
 D 
 
 .17 
 
 28 
 
 1 49 
 
 5.01 
 
 12.06 
 
 17.64 
 
 30 95 
 
 42.83 
 
 I 
 
 13 
 
 C 
 
 19 
 
 29 
 
 1 41 
 
 4.42 
 
 11.41 
 
 19.65 
 
 32.67 
 
 43 01 
 
 f 
 
 14 
 
 B 
 
 14 
 
 19 
 
 0.78 
 
 2 03 
 
 4 11 
 
 7.36 
 
 14 15 
 
 20.89 
 
 Manzanillo... ( 
 
 15 
 
 A 
 
 0.17 
 
 0.23 
 
 0.67 
 
 2.48 
 
 3.88 
 
 6.98 
 
 13 64 
 
 20.65 
 
 16 
 
 D 
 
 14 
 
 0.25 
 
 0.74 
 
 2 71 
 
 6.43 
 
 10.82 
 
 19.55 
 
 28.95 
 
 I 
 
 17 
 
 C 
 
 0.16 
 
 0.25 
 
 73 
 
 2.08 
 
 5.94 
 
 9 90 
 
 19.02 
 
 24.44 
 
 * The measurements were made in April of each year. 
 
 t Replants are omitted in averages for the years 1924 to 1928 inclusive but are included in those of 
 1929, 1930, and 1931. 
 
 t Trees 1, 3, 5, and 7 were removed from rows 2 and 4 in April, 1931. The figures given for these rows 
 in the 1931 column are the averages of the remaining trees. 
 
 trees (systems C and D, rows 17 and 16). Representing the size by the 
 cross-section area of the trunk and taking D as 100 per cent in each year, 
 the mean size of the trees of A and B for the years 1927 to 1931, inclu- 
 sive, is respectively 83, 63, 67, 71, and 72 per cent. The cause of this differ- 
 ence is not evident. 
 
 The severely pruned Ascolano trees of row 11 made less growth than 
 did the other trees of this variety. This difference in growth increased as 
 the trees became older and in 1931 the average cross-section area of the 
 trunks of the severely pruned trees was only 53 per cent of that of the 
 average of the other Ascolano trees. 
 
 Height and Spread of the Trees. — Height and spread measurements 
 
Bul. 568 
 
 Effect of Pruning Young Olive Trees 
 
 19 
 
 were obtained for each year but only those taken at the end of the seventh 
 year need be summarized. Table 5 shows the average height and spread 
 of the trees of each row in 1931 — the end of the seventh year — and also 
 
 7S 
 
 Legehd 
 
 /9i4 /92S /926 /927 /9£S /929 /9S0 /93I 
 Fig. 10. — Growth of olive trees under systems A, B, C, D, and E 
 as shown by the cross-section areas of the trunks. The varieties are 
 plotted separately but on the same scale showing average trunk 
 cross-section areas in square inches for each year. 
 
 the product of the average spread multiplied by the average height. 
 These figures do not show any appreciable differences in height or spread 
 of Mission, Sevillano, or Ascolano trees primed according to systems 
 
20 
 
 University of California — Experiment Station 
 
 . 1 . />', C, or D. The severely pruned trees of row 11 (system E) are con- 
 siderably smaller than those of the other four rows of Ascolano. It 
 appears that the Manzanillo trees of rows 16 and 17 under pruning 
 systems D and C are slightly taller than the trees of rows 14 and 15 
 which are under pruning systems B and A, respectively, but they have 
 the same spread. 
 
 TABLE 5 
 
 1 1 BIGHT AND SPREAD OF THE TREES AT THE END OE SEVEN YEAKS 
 
 (Averages of the trees of each row) 
 
 Variety 
 
 Row 
 
 Pruning 
 system 
 
 Height, 
 feet 
 
 Spread, 
 feet 
 
 Height X spread, 
 square feet 
 
 Mission ' 
 
 / 
 
 1 
 2 
 3 
 4 
 
 5 
 6 
 
 7 
 8 
 
 9 
 
 10 
 11 
 12 
 13 
 
 14 
 15 
 16 
 17 
 
 A 
 B 
 
 C 
 D 
 
 A 
 B 
 C 
 
 n 
 
 A 
 B 
 K 
 D 
 C 
 
 B 
 A 
 D 
 C 
 
 18.7 
 
 19 
 
 14 4 
 14 1 
 
 14 4 
 14 .1 
 
 15 1 
 
 15 4 
 
 8 5 
 14 8 
 14 4 
 
 10.8 
 
 9 8 
 12 5 
 11.8 
 
 Trees removed 
 
 14.8 
 Trees removed 
 
 15 7 
 
 14 1 
 14 1 
 
 13 4 
 
 13 .8 
 
 14 4 
 14.8 
 
 8 2 
 14 1 
 14.1 
 
 11.2 
 11.8 
 
 11.8 
 11.8 
 
 275.5 
 
 299.1 
 
 203 4 
 199.1 
 
 Ascolano ■ 
 
 \ 
 
 193.7 
 194 7 
 
 217.4 
 227.0 
 69.9 
 208.7 
 203.4 
 
 120.5 
 116.2 
 
 
 I 
 
 147.4 
 139.9 
 
 Crop. — There was no crop in 1927 — the fourth season after plant- 
 ing — except a few scattered fruits on unpruned trees. In 1928 the 
 unpruned trees (system A) bore a small crop; the lightly pruned trees 
 (systems B, C, and D) a very light crop; and the severely pruned trees 
 (system E) none. Spring frost reduced the 1929 crop. In 1930 the first 
 crop of commercial importance was produced. The Sevillano, Ascolano, 
 and Manzanillo varieties were harvested and graded. The Missions were 
 frozen before they matured and were not harvested. Table 6 gives the 
 average weight of crop for the trees of each row for 1928 to 1930, and 
 the percentage of large-sized fruits in the 1928 and 1930 crops. 
 
 In 1928 the unpruned trees outyielded all others. This crop, however, 
 was too small for the differences to be of much practical value. The 1929 
 and subsequent crops were not greatly different on the trees of any 
 single variety under pruning systems A, B, C, and D. The severely 
 
Bul. 568] Effect of Pruning Young Olive Trees 
 
 21 
 
 pruned Ascolano trees of row 11 did not produce a crop of commercial 
 importance within the 7-year period of the experiment. 
 
 Influence of the Variety. — Figure 10 shows the growth of the trees 
 during the 7 years (except for two rows of Missions which were re- 
 moved ) . 
 
 TABLE 6 
 
 Summary of Crop Records 
 (Averages of the trees of each row for each year expressed in pounds) 
 
 
 
 Row 
 
 Pruning 
 
 system 
 
 1928 
 
 1929 
 
 1930 
 
 Total 
 
 Variety 
 
 Average 
 weight 
 per tree 
 
 Per cent* 
 large size 
 
 Average 
 
 weight 
 
 per treef 
 
 Average 
 weighty 
 per tree 
 
 Per cent 
 large size 
 
 of 3 crops, 
 average 
 weight 
 per tree 
 
 
 1 
 
 1 
 
 A 
 
 29.9 
 
 67 
 
 33 .2 
 
 
 
 
 Mission 
 
 
 2 
 
 B 
 
 14 .7 
 
 53 
 
 29 
 
 
 
 
 
 ) 
 
 3 
 
 C 
 
 16.9 
 
 53 
 
 39.2 
 
 
 
 
 
 1 
 I 
 
 4 
 
 D 
 
 17.8 
 
 51 
 
 46.4 
 
 
 
 
 
 f 
 1 
 
 5 
 
 A 
 
 15.8 
 
 76 
 
 19.4 
 
 61.2 
 
 72 
 
 96.4 
 
 Sevillano .., . 
 
 ) 
 
 6 
 
 B 
 
 4.6 
 
 88 
 
 11.0 
 
 57.4 
 
 81 
 
 73.0 
 
 
 I 
 
 7 
 
 C 
 
 3 3 
 
 80 
 
 8.8 
 
 53 
 
 72 
 
 65.1 
 
 
 8 
 
 D 
 
 3.5 
 
 91 
 
 14.7 
 
 55 .0 
 
 73 
 
 73.3 
 
 
 f 
 
 9 
 
 A 
 
 24 
 
 65 
 
 31.0 
 
 74 1 
 
 73 
 
 129.1 
 
 
 10 
 
 B 
 
 11.9 
 
 62 
 
 22.7 
 
 72.2 
 
 74 
 
 106.7 
 
 Ascolano 
 
 \ 
 
 11 
 
 E 
 
 
 
 
 
 
 8.6 
 
 77 
 
 8.6 
 
 
 1 
 
 12 
 
 D 
 
 3.7 
 
 71 
 
 18 
 
 72 2 
 
 75 
 
 93.9 
 
 
 ! 
 
 13 
 
 C 
 
 7.5 
 
 60 
 
 11.7 
 
 75.9 
 
 73 
 
 97 .2 
 
 
 f 
 
 14 
 
 B 
 
 4 4 
 
 88 
 
 6 
 
 19 4 
 
 91 
 
 24 4 
 
 Manzanillo. 
 
 •J 
 
 15 
 
 A 
 
 5.9 
 
 86 
 
 2.6 
 
 22 9 
 
 86 
 
 31.5 
 
 
 ) 
 
 16 
 
 D 
 
 2 9 
 
 90 
 
 1.8 
 
 33.0 
 
 93 
 
 37.6 
 
 
 { 
 
 17 
 
 C 
 
 2.6 
 
 94 
 
 2 
 
 21 1 
 
 95 
 
 25.7 
 
 * Per cent large size indicates the percentage, by weight, of the fruit which in short diameter exceeded 
 the measurements as follows: for Mission 10/16 inch; for Sevillano 25/32 inch; for Ascolano 25/32 inch; 
 for Manzanillo 11/16 inch. 
 
 t The 1929 crop was not graded. 
 
 J The 1930 crop of Mission was frozen before maturity and was not harvested. 
 
 By 1$30 the mean growth of the Manzanillo under all systems was 
 only about one-half that of the Sevillano and Ascolano, while the growth 
 of the Mission was about a third greater than these. The Manzanillo is 
 naturally a slow grower but the more rapid growth of the Mission is 
 due only in part to any inherent quality it may have in this respect. The 
 Mission trees were older and larger when planted than were the other 
 varieties after two years growth in the field. The greater development 
 of the Mission trees is therefore apparently due to the larger size of the 
 trees when planted. They were of about the same size in 1929 as the 
 Sevillanos and Ascolanos were in 1930; and in 1930 the Missions were as 
 large as the Sevillanos and Ascolanos were in 1931. 
 
22 
 
 University of California — Experiment Station 
 
 Influence of the System of Pruning. — The retardation of growth 
 caused by heavy pruning is clearly shown by the trees under system E 
 when these are compared with the other Ascolano trees under systems 
 A, B, C, and D. When planted, the trees were of similar size (see table 1 ) . 
 In 1927 the cross-section area of the trunks of the severely pruned trees 
 
 
 
 |fe 
 
 
 M 
 
 
 fliiP^i '' r 
 
 
 
 
 
 
 m. 
 
 
 
 '^m 
 
 
 
 
 mm 
 
 
 • •.■; X'^ v '•'' ^ ~ 
 
 
 9 
 
 p 
 
 
 
 B36ffiESa£^ 
 
 ifr 
 
 * ~ **$sXy* ' 
 
 
 :, 
 
 Fig. 11. — Manzanillo tree 5 years old having had no pruning. 
 Illustrates system A before pruning in 1929. 
 
 was only 77 per cent of the average of the unpruned and lightly, pruned 
 trees of the same variety, and fell to 67 per cent, 63 per cent, 54 per cent, 
 and 53 per cent during the succeeding years. They bore no crop until 
 1930 and then only 8.6 pounds per tree which was 11.7 per cent of the 
 mean crop of the other Ascolano trees of that year. The Mission, Sevil- 
 lano, and Ascolano trees under system A grew more rapidly than those 
 under systems B, C, and D prior to the opening up and thinning-out 
 process begun in 1929 and completed in 1930. Following this heavy 
 pruning the rate of growth of the trees under system A decreased rela- 
 tively to that of the trees under systems B, C, and D, and in 1931 there 
 were no considerable differences in size. The rate of growth of the Mis- 
 
Bul. 568] 
 
 Effect of Pruning Young Olive Trees 
 
 23 
 
 sion, Sevillano, and Ascolano trees under systems B, C, and D was not 
 greatly different at any time during the investigation (fig. 10 and 
 table 4). 
 
 The Manzanillo trees under system D grew faster after 1927 than did 
 the trees of this variety under any other system. It is not clear why 
 
 Fig. 12. — The same Manzanillo tree as shown in figure 11, after 
 pruning in 1929. Illustrates system A after pruning. 
 
 these annually pruned trees showed a greater growth than those under 
 system A which were unpruned until 1929. 5 The crop on all of the Man- 
 zanillo trees prior to 1930 was very light and in that year the trees under 
 system Z> outyielded those under any other system. 
 
 All of the trees of the Mission, Sevillano, and Ascolano varieties were 
 well shaped at the end of the pruning experiment. The distribution of 
 the scaffold branches on the trunk was best on the annually pruned trees 
 
 5 A possible explanation of the better growth of the annually pruned trees might 
 be in their changed habit of growth. The unpruned trees were bush-like in character 
 and the branches were long and drooping. The annually pruned trees were more 
 upright in growth. It is well known that bending the branches of woody plants tends 
 to check their growth. 
 
24 
 
 University of Calibx)Rnia — Experiment Station 
 
 (systems C and D). The main branches of the Mission trees which were 
 opened up by heavy pruning in 1929 (systems A and B) were slightly 
 more spreading than those of the annually pruned trees (systems C and 
 D) . (Compare figures 2 and 3.) The Sevillano and Ascolano trees showed 
 little or no advantage in shape of tree of one pruning system over any 
 
 Fig. 13. — Manzanillo tree 5 years old shaped by tying and light 
 annual pruning. Thinning the laterals on the main branches has 
 lessened their tendency to droop. Illustrates svstem D after pruning 
 in 1929. 
 
 of the others. Figure 4 shows a five-year-old Ascolano tree of system A 
 before pruning and figure 5 shows this same tree after pruning in 1929. 
 One of the five-year-old Ascolano trees lightly pruned annually is shown 
 in figure 6. The annually pruned Manzanillo trees (systems C and D) 
 were slightly taller and more upright than those pruned only once 
 (system A) or twice (system B) which tended to be bush -like in shape 
 during the first five years in the orchard (fig. 11; this same tree after 
 pruning is shown in figure 12.) This difference was pronounced in 1929 
 
Bul. 568] Effect of Pruning Young Olive Trees 25 
 
 but less striking in 1931. The Manzanillo trees of system D which had 
 been supported by tying and internal bracing appeared to be better 
 shaped in 1929 than those of system C which had not been tied. Figure 
 13 shows a Manzanillo tree formed by annual pruning and tying. How- 
 ever, this difference was not apparent in 1931 or later and it appears 
 doubtful that any permanent advantage resulted from the tying or 
 bracing. The trees of the other three varieties showed little or no differ- 
 ence in this respect between systems C and D. 
 
 The shaping of the trees mainly by a single heavy pruning (systems 
 A and B) resulted in many large pruning wounds on the trunks and 
 scaffold branches of the trees. However, the wounds healed rapidly. The 
 trees lightly pruned annually (systems C and D) were nearly free from 
 large wounds. Careful examination in April, 1933, failed to disclose any 
 evidence of decay in any of the trees under systems A, B, C, and D. 
 
 The trunks of the severely pruned trees (system E) sunburned on the 
 southwest side. Wood-rot fungi obtained entrance through the sun- 
 burned areas and when examined in April, 1933, every trunk of the 
 severely pruned trees was badly decayed. The heartwood of several of 
 the trunks was almost completely destroyed. 
 
 SUMMARY AND CONCLUSIONS 
 
 The slower development of the severely pruned Ascolano trees (sys- 
 tem E) as compared with that of Ascolano trees less severely pruned 
 clearly demonstrates the depressing effect of heavy pruning on young 
 olive trees of this variety. The limitation of leaf surface not only dimin- 
 ished photosynthesis but exposed the trunk to the hot rays of the sun 
 with consequent sunburn and fungus decay. 
 
 The depressing effect of the single severe pruning necessary to shape 
 and thin the trees that were unpruned until 5 years old (system A) was 
 approximately the same as the depressing effect of five light annual 
 primings (system C) . The total weight of the removals in each of the two 
 cases was also roughly the same for the Mission, Sevillano, and Ascolano 
 varieties. The Manzanillo trees lightly pruned annually, on the contrary, 
 appear to have developed faster than those left unpruned for three or for 
 five years and this despite the fact that the total weight of removals 
 was greater. 
 
 The form of the trees at the end of 7 years was not greatly different 
 whether shaped by light annual pruning or by heavy pruning during the 
 fifth year (or fifth and sixth years). Perhaps the Mission trees shaped 
 mainly by a single pruning the fifth year were slightly superior in form 
 
26' University of California — Experiment Station 
 
 to those shaped by annual pruning. On the other hand annual pruning 
 produced slightly better-shaped Manzanillo trees (7 years old) than 
 were obtained by one or two prunings. No considerable advantageous 
 differences in form attributable to the pruning could be observed among 
 the Ascolano and Sevillano trees. 
 
 Many large pruning wounds resulted from shaping the trees mainly 
 by a single pruning (systems A and B). The wounds healed rapidly, 
 however, and no decay was observed. The trees lightly pruned annually 
 were nearly free from large wounds. Wood-rot fungi entering through 
 sunburned areas caused much decay in the trunks of the severely pruned 
 Ascolano trees. 
 
 The trees left unpruned until 5 years old bore heavier crops in the 
 fifth season than did the pruned trees. The crops during the sixth and 
 subsequent years were about the same on the trees of each variety under 
 all systems except severe pruning. The severely pruned trees did not 
 produce a crop of commercial importance during the seven years. 
 
 Artificial supports of the types used in the D system produced little 
 or no permanent improvement in the form of the Mission, Sevillano, or 
 Ascolano trees. Tying up the branches of the Manzanillo trees by passing 
 a band of burlap cloth around the tree and supplementing this with in- 
 ternal bracing of the main scaffold branches produced a marked im- 
 provement in the shape which was apparent for at least five or six years. 
 At seven years of age, however, the difference between the trees which 
 had been tied and those not tied was not great and it appears doubtful 
 that any permanent improvement has accrued from the tying. 
 
 ACKNOWLEDGMENTS 
 
 The plan of the experiment was originated by Professor F. T. Bioletti 
 who also rendered valuable assistance in the preparation of the manu- 
 script. 
 
 The cultural work was mostly done by Mr. G. Barovetto who also 
 assisted in the planting, pruning, and measuring of the trees. 
 
 13m-2,'34