Pruning is the most important aspect of grapevine maintenance. If a grapevine produces too many grape clusters, the fruit will not ripen. Pruning helps grapevines to produce a manageable amount of fruit. Approximately 90 percent of the total mass of a grapevine should be removed at the end of each winter. This includes all growth except for year-old side shoots and short canes that will grow into first-year growth the next season.
Determine which one-year-old fruiting vines and buds you will leave to develop into next year's canes (renewal spurs) and tie a brightly colored piece of cloth to these vines.
Prune away any vine that has not been selected to remain.
Weigh these vines.
Calculate the number of buds to leave on a cane based on the weight of the vines you removed. Add 30 buds for the first pound of pruned vine weight and another 10 buds per pound to the total.
Subtract the number of buds left on your renewal spurs from this total. Divide the rest of the buds between the canes. For example, if you figure to leave 40 buds on a vine with four side shoots, then subtract four spurs with two buds each. Then divide the remaining 32 buds by four canes for eight buds per cane.
Prune your canes to the correct length by removing the rest of the canes at the point where a bud emerges from the cane (a node).