Pruning grapevines can be a confusing process because of the different pruning goals during different stages of the grapevine's life. Once the two-year training process is completed, pruning settles into a routine. Understanding the pruning goals of each stage of training will help get rid of the confusion and simplify the process.
The purpose of pruning is to train the vines into an orderly growth pattern and optimize grape production. Pruning helps avoid over-burdening the vines with an excessive crop, and promotes healthy vine and vegetation growth. Prune vines during the dormant season, in late winter or early spring.
Adopt a training system suitable for the support that you have available. The most popular training system for home gardeners is the four-cane Kniffin system. This system is designed for a fence or trellis with two horizontal wires or supports. Adapt these instructions to fit your situation.
Cultivate the trunk during the first year after planting. Allow the vine to grow until it reaches above the top wire of the trellis. Pinch back the top.
Choose eight canes to become the lateral cordons in the late winter or early spring of the second year. Remove all other canes. Train two canes growing in each direction on each wire of the trellis.
Cut back one cane of each pair to one or two buds. These short canes will become renewal spurs for the next years crop.
Prune the long canes on each wire back, leaving 8 to 13 buds on each cane, depending on the vigor of the vine. Less vigorous vines should have fewer buds remaining.
Prune the old wood back during the dormant season each winter, allowing the renewal spur to develop for the next crop. The vines need to be vigorously pruned each year, leaving 45 to 60 buds, depending on the vigor of the vine.