Growers of all fruits soon learn that excessive vegetative vigor is not usually accompanied by fruitfulness. Too great vigor is indicated by long, leafy, unbranching shoots. Some fruit-growers go so far as to say that fruitfulness is inversely proportionate to vegetative vigor. There are several methods of diminishing the vigor of the vine; as, withholding water and fertilizers, stopping tillage, the method of training and by pruning. Pruning is used to decrease the vigor of the vine, in theory at least, for the practice is not always so successful, by pruning the roots or by summer-pruning the shoots.
Root-pruning the grape at intervals of several years is a regular practice with some varieties in warm countries, Europe more especially, but is seldom or never practiced in America except when planting and when roots arise from the cion above the union of stock and cion.
Summer-pruning to induce fruitfulness consists in removing new shoots with newly developed leaves. These young shoots have been developed from reserve material stored up the preceding season, and until they are so far developed that they can perform the functions of leaves they are to be counted as parasites. When, therefore, these shoots are pruned or pinched away, the plant is robbed of the material used by the lusty shoot which up to this time has given nothing in return. The vigor of the plant is thus checked and fruitfulness increased. Summer-pruning may become harmful if delayed too long. The time to prune is past with the grape when the leaves have passed from the light green color of new growth to the dark green of mature leaves.
Fruit-bearing may be augmented by bending, twisting or ringing the canes, since all of these operations diminish vegetative vigor. Ringing is the only one of these methods in general use, and this only for some special variety or special purpose, and usually with the result that the vigor of the vine is diminished too much for the good of the plant. Ringing is discussed more fully in Chapter XVI.
_The manner of fruit-bearing in the grape._
Before attempting to prune, the pruner must understand precisely how the grape bears its crop. The fruit is borne near the base of the shoots of the current season, and the shoots are borne on the wood of the previous year's growth coming from a dormant bud. Here is manifested one of Nature's energy-saving devices, shoot, leaves, flowers and fruit spring in a short season from a single bud. In the light of this fact, pruning should be looked on as a simple problem to be solved mathematically and not as a puzzle to be untangled, as so many regard it. For an example, a problem in pruning is here stated and solved.