“With the ends of the fingers and the help of the thumb-nail, it is customary to pinch off from the too vigorous side the tips of the young branches while they are still tender. This operation we may call pinching. The sap that would have been used for the development of these branches is diverted from its course and carried toward the weak shoots, which it renews and stimulates. If the weak side itself needs pinching to arrest shoots that impair the desired symmetry, the operation is postponed as long as possible, while on the strong side it is carried out very early. The sap thus turned away from the vigorous side toward the ailing one has a whole season in which to restore the lost equilibrium.
“Instead of limiting ourselves to pinching off the tips of the young shoots with our thumb-nail, we can suppress them altogether while they are still tender. This is done as early as possible on the strong side, only the indispensable shoots being left. If it is necessary on the weak side, it is not done until the latest possible moment. This operation we may style bud-nipping, since the word ‘bud,’ by which we designate the germ of the future branch when it is still enveloped in scales, applies also for the sake of convenience to the branch already developed but still young and tender. It is evident that nipping off the buds from the strong part tends, [[122]]even more than pinching, to promote the desired growth of the weak part. The more branches we suppress entirely, the fewer will be left to share the sap needed by the branches we wish to strengthen.
“What turns aside the sap from the part pruned, pinched, or nipped, toward the part left intact, is evidently the more or less complete suppression of foliage. It is primarily the leaves that by the continual evaporation of which their surface is the seat determine the ascent of the liquid drawn from the soil by the roots. The more numerous these leaves are at any one point, the more abundant the flow of sap to that point; the scarcer they are, the less the flow of sap. To diminish at any point the number of leaves by pinching, bud-nipping, or any other means, is therefore to diminish at the same point the flow of sap, which will go in some other direction, to the parts that have more leaves and hence a more rapid rate of evaporation to summon the sap. It is plain, then, that a middle course may be followed between the pinching that partly suppresses the foliage of a young branch and the bud-nipping that suppresses it entirely. This middle course consists in cutting a certain number of leaves from the too vigorous shoots; and they should be cut clean without tearing, by severing the stem and leaving its base undisturbed.
“The easiest way for the sap to run from the roots to the foliage is from bottom to top in a vertical line. Anything that interferes with this course hinders also the upward impetus. Thus in branches [[123]]with sharp elbows and abrupt bends the rush of sap is slackened just as the rate of flow of a water-current is diminished by the windings occurring in its bed. Thus, again, in a branch having a decided incline downward the sap moves with difficulty, because its movement toward the extremity of this branch is in a direction contrary to that which is natural to it. The application of this principle is evident. If we wish to moderate a too vigorous growth of branches, we bend them toward the ground; if we wish to stimulate a too feeble growth, we straighten up the branches until they assume a vertical posture.
“We can also turn to account the exhausting effect of fruit-bearing. The more fruitful a branch is, the weaker it becomes, since the use of sap in fruit means so much the less for foliage, and it is foliage that invigorates the branch. Accordingly we will leave the greatest possible quantity of fruit on the strong part of our tree, and suppress it on the weak part.” [[124]]
CHAPTER XXVI
MAKING FRUIT TREES BEAR
“If one side of a tree is pruned very short and the other very long, the natural course of the sap is to some extent diverted from the first side toward the second, which is richer in buds and consequently in foliage. We have just seen how this principle is utilized to check the growth of too vigorous a part in order to stimulate that of one that is too feeble and thus redress the balance between the two. But what would be the result if the whole tree were pruned at once?
“Let us first see what takes place in a single branch. Pruned long, it preserves the greater part of its buds, all of which call for nourishment from the sap flowing in that direction; pruned short, it keeps only a few buds, which having the sap of the entire branch at their disposal, will receive each a supply that is superabundant in proportion to the fewness of the buds. For example, what twelve would ordinarily have had for consumption, two or three will now have to themselves; and because of this superabundance of nourishment each bud will develop much more vigorously than it would otherwise have done. Hence if the whole tree is pruned with an unsparing hand, all the sap drawn from the [[125]]soil by the roots, having no longer a tendency to go to one side rather than the other, will be distributed evenly; and the few buds left intact by the pruning-shears will show a luxuriance of growth in proportion to the supply of nourishment placed at their disposal. Thus thorough pruning applied to the whole tree has the effect of giving it new vigor, of rejuvenating it in some measure, or, in other words, of replacing its worn-out branches with vigorous ones. Accordingly when a tree has become exhausted by abundant fruit-bearing, it is pruned without stint one year in order to restore its vigor of growth.