Page 6 



BETTER FRUIT 



The Value of Thinning 



By Clayton L. Lone. Extension Horticulturist, Oregon Agricultural College 



July, 1921 



THINNING apples in the early 

 summer will do more to in- 

 crease the size and color of the fruit 

 and the total value of the crop than 

 any other operation supplementary 

 to common orchard practices. It is 

 also the most satisfactory as well 

 as profitable way to' prevent loss of 

 branches from breakage on trees 

 bearing full crops. Although it will 

 not increase the vigor of the tree, it 

 will be a very important factor in 

 maintaining that which the tree al- 

 ready has. 



The activity of an apple tree, whether 

 for fruit-bud formation, fruit production or 

 growth is controlled largely by the relation- 

 ship of the raw food materials as furnished 

 by its environment and utilized by itself. 

 The soil furnishes the moisture and "soil 

 foods" and the atmosphere furnishes the 

 "air foods." If the rainfall is ample or 

 irrigation practiced, the soil properly 

 drained yet capable of holding moisture, 

 and excessive evaporation prevented by 

 proper cultivation or mulching, the soil 

 moisture will not be the limiting factor. If 

 these conditions are not right, and a uni- 

 form moisture supply is not available dur- 

 ing the growing season, this is where our 

 first attention is needed. 



If the soil needs draining, this should 

 come first and nothing else can take its 

 place. If it will not retain enough water to 

 mature the crop, organic matter should be 

 incorporated and other means of increas- 

 ing the water holding capacity of the soil 

 practiced. If these corrections, together 

 with preventation of evaporation from the 

 surface soil, do not supply the tree with a 

 sufficient supply of moisture, a condition 

 often met in unirrlgated, semi-arid sec- 

 tions, nothing can be done other than that 

 of reducing the top of the tree by pruning 

 to fit this shortage. 



After this moisture supply is made to fit 

 the tree or the tree to fit the moisture, our 

 next step is to properly balance the two 

 groups of foods, the soil foods and the air 

 foods, to bring about such activity of the 

 tree as is desired. If the soil is thin or worn 

 out, which usually means low in organic 

 matter, the soil foods may be the limiting 

 factor and should be given next considera- 

 tion. Annual application of nitrogen will 

 be a temporary remedy, but the incorpora- 

 tion of organic matter, by plowing down 

 straw, rough manure, cover crops, etc., are 

 necessary in any long time solution of this 

 soil problem. The nitrogen of the soil, 

 which is the limiting factor in the group 

 of soil foods, is carried in the organic matter 

 of the soil and can be maintained only by 



annual contributions of organic matter 

 forming materials. The growing of catch 

 crops should be an annual practice in culti- 

 vated orchards. 



THE "air foods" are abundant in propor- 

 tion to the area of leaf surface of the 

 tree, together with the strength of the light 

 playing upon this leaf surface. These foods 

 may be the limiting factor where the soil is 

 extremely fertile or the orchardist a heavy 

 pruner or where a combination of the two 

 exist. In this case the remedy would be 

 a slowing up of the pruning, excepting a 

 light thinning out in very dense trees, and 

 a withdrawal of all nitrogenous fertilizers, 

 manures and leguminous cover-crops. In 

 other words let the tree accumulate a larger 

 leaf surface and do not add nitrogen to the 

 soil. This condition is seldom met in ma- 

 ture trees as their usual lack of vitality 

 shows. Most mature trees would be more 

 productive of profits if their vigor was con- 

 siderably increased. 



Thinning of the fruit becomes necessary 

 whenever the activity of the tree is too 

 largely consumed in the formation of fruit 

 buds and the production of fruit at the ex- 

 pense of wood growth, a condition brought 

 about by an over supply of air foods as com- 

 pared to the soil foods. The young, vigor- 

 ous tree comes into partial bearing, then into 

 full bearing and finally over-bears before 

 it is forced into the habit of alternate bear- 

 ing. A tree that overbears is under-vigorous 

 and carries a large number of very slow- 

 growing fruit spurs that seldom bloom and 

 when they do bloom never set fruit, another 

 large number that bloom and bear and very 

 few that are vigorous, making a good 

 growth, that do not bloom. 



Practically all apple trees that are consist- 

 ent annual bearers have 25 per cent or more 

 of their fruit spurs too vigorous each year 

 to form fruit buds. This will insure enough 

 vigor in the tree as a whole to make a good 

 annual growth with a good number of new 

 spurs forming fruit buds on the one year 

 old wood. This condition cannot be brought 

 about in over-bearing trees by thinning the 

 fruit, no matter how severe the treatment. 

 The trouble is more deeply seated than this 

 year's crop of fruit. It is an unbalanced re- 

 lationship of the "soil foods" and the "air 

 foods" with the latter greatly predominat- 

 ing. This unbalanced condition may be of 

 short or long standing, but continually 

 growing worse as the natural tendency of 

 the tree is to increase rather than to 

 diminish it. 



In fact this plight may become so ex- 

 treme that the tree will get beyond this 

 alternate bearing stage to a seldom bearing 

 or even to a never bearing stage. Artificial 

 means that tend to increase the "soil foods" 

 and decrease the "air foods" must be used 



and used strenuously. The natural ten- 

 dency of the tree must be overcome, the un- 

 balanced relationship of these two groups 

 of foods must be rectified and the accumu- 

 lation of the over-abundant "air foods" of 

 previous years must be matched. The com- 

 bined influence of pruning, fertilizing, 

 cultivating and cover-cropping (or mulch- 

 ing), and thinning at their very best will 

 be required to get this tree out of its alter- 

 nate bearing habit back into the proper stage 

 of vigor. 



It will be a much harder task to get old 

 trees out of their alternate bearing habit 

 than it will be to keep young, vigorous trees 

 from getting into it. In either case the ten- 

 dency of the tree will have to be fought 

 against annually. 



THE effects of thinning may be a big 

 factor in keeping young, vigorous trees 

 from forming the alternate bearing habit, 

 but it is not enough to get trees with the 

 habit established back into annual bearing. 

 It will help to conserve the vigor already 

 there, but it will not instill new vitality into 

 the tree. The greatest benefit jrom thin- 

 ning will be on this -gear's frtdt. It will pay 

 big dividends on the increased size and 

 color of the fruit and continue to pay for 

 years to come on the branches saved from 

 the breaking that so often takes place in 

 heavily loaded trees. Time will be saved in 

 the picking, grading and packing of the 

 crop equal at least to that required for 

 thinning. 



The most economical time to do this 

 thinning is immediately after the June 

 drop, after nature has done her thinning. At 

 this time most of the apples left will ma- 

 ture and one need not hesitate to do all 

 necessary thinning at one time. It is far 

 cheaper to remove all surplus fruit the first 

 time over the trees, than it is to make two 

 or more thinnings. In practice all imperfect 

 fruit should be removed. Each cluster 

 should be reduced to not more than one 

 fruit and then enough others removed un- 

 til those remaining are at a desirable dis- 

 tance apart. Variety as well as vigor of the 

 tree should be considered in determining 

 the right distance apart to leave the fruit. 

 On vigorous trees the smaller varieties will 

 net most if left six or seven inches apart 

 while eight or ten is none too far for the 

 large varieties. These distances should- be 

 increased an inch or two whenever the tree 

 shows lack of vigor. 



The time required to do this work will 

 vary with the size of the tree, as well as set 

 of fruit. Trees capable of bearing three 

 or four boxes of marketable fruit will re- 

 quire about one-half hour, those equal to 

 ten boxes in the neighborhood of one hour 

 {Concluded on fage 16) 



