BETTER FRUIT 



AN T 



LLUSTRATED MAGAZINE PUBLISHED MONTHLY IN THE INTEREST OF MODERN. PROGRESSIVE FRUIT GROWING AND MARKETING 



Pruning for Size 



By V. R. Gardner, of Experiment Station, Corvallis, Oregon— Address Delivered at Fruit Growers' Conference, Tenth National Apple Show, Spokane 



THE intelligent fruit grower is in- 

 terested not only in what consti- 

 tutes good orchard practice, — not 

 only in what are the various operations 

 that should be performed, the things 

 that should be done, and in how and 

 when they should be done, — but he is 

 interested also in how these practices 

 operate, in how each and every one of 

 them influences the growth of the tree 

 itself and the development of its fruit. 

 At least this is the attitude of the mod- 

 ern scientific fruit grower — the one 

 who regards his work as something 

 more than simply a trade. If the ques- 

 tion under consideration is that of irri- 

 gation he is not satisfied simply with a 

 knowledge of how frequent and how 

 heavy applications are required for his 

 conditions, but he is interested in the 

 role that water plays in the normal 

 functioning of the tree and in the nor- 

 mal development of its fruit, in the 

 minimum as well as the optimum water 

 requirements of the plant, and in many 

 other related questions. It is only as 

 he possesses this general, and at the 

 same time specific, information re- 

 garding his various orchard practices 

 that he is able intelligently to modify 

 them to meet emergencies. That the 

 grower today really is interested in 

 these more serious, more scientific, 

 phases of orchard management, is evi- 

 denced by the demands that continu- 

 ally are being made upon college ex- 

 periment station men for information 

 upon such subjects as the one an- 

 nounced as the topic of this article, 

 "Pruning for Size." It is true that there 

 is still a great demand for empirical 

 knowledge, — as rules for pruning, for- 

 mulae for fertilizers, definite spraying 

 calendars; and information of this type 

 will probably continue to be of great 

 use. Today the demand is for a prun- 

 ing method or pruning system that will 

 increase size; tomorrow it may be for 

 a method that will heighten color; still 

 later it may be for a method that will 

 help control fruit pit or rosette. It is 

 well that this information be made 

 available in the form of rules or direc- 

 tions if it is to be had. It is better if 

 there comes to be a more general un- 

 derstanding of growth processes and 

 of the ways in which they may be con- 

 trolled or modified. With these general 

 considerations in mind let us make a 

 somewhat careful analysis of pruning 

 practice to see in what way or ways it 

 most directly affects the growth of the 

 tree and the development of its fruit. 

 Incidentally we shall see whether it 

 directly or indirectly influences size. 



In the first place it may be well to 

 call attention to the fact that, broadly 

 speaking, the object of any and all of 



the orchard operations is: (1) to in- 

 crease yield, (2) to improve quality or 

 grade, (3) to lower cost of production. 

 It is evident that certain orchard opera- 

 tions contribute almost exclusively to a 

 single one of these general objects. For 

 instance, orchard heating is practiced 

 not to lower cost of production, nor to 

 increase the grade of fruit, but pri- 

 marily to increase yield — or at least to 

 make yields more certain. On the other 

 hand, certain other orchard operations 

 contribute to the realization of two or 

 more of these general objects of all 

 orchard practice. Irrigation is plainly 

 not employed to lower cost of produc- 

 tion, but in the first place to improve 

 grade through increasing size, and in 

 the second place to increase total yield. 

 Now the question arises, "Is pruning a 

 practice whose aim is mainly to lower 

 production costs, to increase yield, or 

 to improve grades?" Increase in size 

 is apt to involve some increase in yield, 

 but primarily it effects an improvement 

 in grade; hence we are mainly inter- 

 ested in the way in which pruning may 

 help us attain that general object. 



There is little, if any, doubt as to the 

 available water supply in the soil being 

 the factor most directly bearing upon 

 the proper sizing of fruit. The apple 

 averages about 85 per cent water in com- 

 position, and this, coupled with the fact 

 that water is found in the soil in the 

 same form as in the fruit, would lead 

 us to assume that there is a very direct 

 relation between the factors of soil 

 moisture and fruit size. That there is 

 a close correlation between water sup- 

 ply and size not only of fruit but of 

 other plant parts as well, is taught by 

 plant physiology. Furthermore, tillage 

 and irrigation practice for centuries 

 furnishes an abundance of evidence 

 upon the subject. If, then, available 

 water supply is the most important 

 factor influencing size, the question 

 may now be raised as to how, if at all, 

 pruning affects the available water 

 supply. Obviously it cannot influence 

 appreciably the water supply in the 

 soil. Can it then affect the water sup- 

 ply available for particular fruits on 

 the tree? It is evident that pruning 

 may result in a thinning of the crop 

 through the removal of more or less 

 bearing wood. This would automatic- 

 ally make available for the rest of the 

 tree a relatively larger water supply 

 and at least theoretically contribute to 

 increased size on the part of that which 

 remains. However, this assumes thai 

 the intake of the roots would not be 

 reduced by the removal of a part of the 

 top and also that the remaining vege- 

 tative portions of the tree would not 

 have an increased water requirement. 



But these are two assumptions that may 

 not be warranted. Evidence on the first 

 assumption is limited, but we are not 

 without evidence on the second. Under 

 normal conditions the leaves use much 

 more water than the fruit. Pruning 

 that would materially thin the fruit 

 crop through a reduction in bearing 

 wood would also tend to stimulate an 

 increased vegetative growth that in 

 turn would make still further demands 

 upon the water supply available to the 

 tree. It is easily conceivable that this 

 greater leaf surface might more than 

 counterbalance in its water demands 

 the amount theoretically released to 

 remaining fruits through a removal of 

 a part of the bearing surface. Exact 

 evidence on this question is limited in 

 amount, but it is sufficient to warrant 

 questioning the practicability of em- 

 ploying pruning as a means thus in- 

 directly to improve size. At least it is 

 uncertain to what extent pruning is 

 efficient in diverting water from a large 

 number of fruits to a smaller number 

 on the same tree. Experimental re- 

 sults obtained at the Missouri Experi- 

 ment Station indicate that medium late 

 or late-summer pruning that removes 

 vegetative growth (leaves and shoots) 

 only may be a means of diverting a 

 larger proportion of the total water 

 intake to the developing fruits and 

 thus directly aiding in their sizing; but 

 even in that case it is seriously ques- 

 tioned if such a pruning practice ac- 

 complishes enough to be really prac- 

 ticable. 



Another factor of probable impor- 

 tance in determining size of fruit is 

 the available food supply in the soil. 

 This can be of influence only indirectly, 

 as the mineral foods of the soil cannot 

 enter into the composition of the fruit 

 at once, but first must be manufactured 

 into elaborated foods (starches, sugars, 

 proteins, acids, etc.). Obviously again, 

 pruning cannot modify the supply of 

 food in the soil and probably only to a 

 limited extent the intake of food by the 

 roots. To the extent that pruning thins 

 the crop through reducing the bearing 

 surface, it makes available, theoret- 

 ically, a larger supply of raw food for 

 each developing fruit. But since this 

 raw food first must be worked over into 

 elaborated foods before the fruit can 

 store and use it, it is necessary to con- 

 sider the influence of pruning upon leaf 

 surface and leaf activity. These are in- 

 fluences about which comparatively 

 little is known at the present time. 

 Some types of pruning result in an in- 

 crease in leaf surface, others result in a 

 decrease. Whether or not there are 

 corresponding increases and decreases 

 in the manufacture of starches, sugars, 



