Grape vines must be pruned heavily to bear good crops. For the first three years after planting, cut off all but six to eight bunches of immature grapes so that energy can go toward strengthening the root system. From the fourth year on, leave half of the bunches on the vine. Training begins at two years but the method varies depending upon the grape variety.
Four-Armed Kniffin System
The four-armed Kniffin system, the easiest for home gardeners, is suitable for European grapes and for most American grapes including ‘Concord’ and ‘Delaware’.
Begin by tying a young vine to a stake to develop a permanent trunk. Stretch two wires, one 30 to 36 inches high and the other 54 to 60 inches high, between posts spaced 5 to 6 feet on each side of the plant. As the vine grows tie it to the wires. When it passes the first wire, pinch off all lower side shoots. Pinch the tip when it extends 1 foot beyond the top wire.
Just prior to the start of growth during the second year, cut the trunk back, severing a bud located just above the top wire. To develop the four arms, remove all side shoots except for one on each side of both wires. Cut these shoots back to two buds. Secure the lateral branches that grow from these buds to the wires.
During the third late-winter pruning season, cut off all but four shoots on each lateral branch. Two shoots will be fruiting canes. Prune them back to 10 buds. Prune back the other two canes more severely to two buds; these will be the renewal spurs that bear fruit during the following year. The fourth winter and every following year, cut off the two long canes that have borne fruit. The four remaining spurs will have sent out several shoots the previous year. Prune the upper shoots into fruiting canes with 10 buds each and keep the lower shoots as renewal spurs with 2 buds.
Spur-pruning is suitable for most European grape varieties including ‘Tokay’, ‘Muscat’, and ‘Malaga’, as well as for the California grape varieties. The exception is ‘Thompson Seedless’, which should be grown by the four-armed Kniffin system.
During the second summer after planting, stretch a wire 30 inches high between two supports on either side of the vine. When the vine climbs about 1 foot above the wire, cut it back so that it is even with the wire. When the top two buds grow, train one along the wire in one direction, the other in the opposite direction. Tie each shoot loosely to the wire.
During the second winter cut off all lateral growth from the two branches, being careful to leave one bud on the stub of each lateral. During the third winter, thin laterals from the two main branches to strong shoots about 5 to 11 inches apart. Cut each lateral back to two buds or spurs.
From the fourth winter on, two canes will grow from each spur and bear fruit, During the next dormant season, cut off the cane farthest from the trunk and shorten the cane closest to the trunk to two buds. Each winter repeat this spur pruning so that the remaining canes arch back toward the trunk as they grow.