Another principle to be mastered is this: A vine should bear only a limited number of clusters,—say from 30 to 80. A shoot bears clusters near its base; beyond these clusters the shoot grows on into a long, leafy cane. An average of two clusters may be reckoned to a shoot. If the vine is strong enough to bear 60 clusters, 30 good buds must be left at the pruning (which is done from December to late February).
The essential operation of pruning a grape vine, therefore, is each year to cut back a limited number of good canes to a few buds, and to cut off entirely all the remaining canes or wood of the previous season’s growth. If a cane is cut back to 2 or 3 buds, the stub-like part which remains is called a spur. Present systems, however, cut each cane back to 8 or 10 buds (on strong varieties), and 3 or 4 canes are left,—all radiating from near the head or trunk of the vine. The top of the vine does not grow bigger from year to year, after it has once covered the trellis, but is cut back to practically the same number of buds each year. Since these buds are on new wood, it is evident that they are each year farther and farther removed from the head of the vine. In order to obviate this difficulty, new canes are taken out each year or two from near the head of the vine, and the 2-year-or 3-year-old wood is cut away.
The training of grapes is a different matter. A dozen different systems of training may be practiced on the same trellis and from the same style of pruning,—for training is only the disposition or arrangement of the parts.
On arbors, it is best to carry one permanent arm or trunk from each root over the framework to the peak. Each year the canes are cut back to short spurs (of 2 or 3 buds) along the sides of this trunk.
Grapes are set from 6 to 8 feet apart in rows which are 8 to 10 feet apart. A trellis made of 2 or 3 wires is the best support. Slat trellises catch too much wind and blow down. Avoid stimulating manures. In very cold climates, the vines may be taken off the trellis in early winter and laid on the ground and lightly covered with earth. Along the boundaries of home lots, where grapes are often planted, little is to be expected in the way of fruit because the ground is not well tilled.
The grape is subject to many insects and diseases, some of which are very destructive. The black-rot is the most usual trouble. See p. 209.
To produce bunches of high quality and free from rot and frost injury, grapes are sometimes bagged. When the grapes are about half grown, the bunch is covered with a grocer’s manila bag. The bags remain until the fruit is ripe. The grapes usually mature earlier in the bags. The top of the bag is split, and the flaps are secured over the branch with a pin; Figs. 278, 279, 280 explain the operation.
