"When gardeners prune, they should remove the majority of wood produced the previous season – until about 90 percent is pruned off," said Strik.
The time to prune grapevines is from January through the first of March, when the grapes are dormant.
There are two types of grape pruning—cane pruning and spur pruning. Mature plants should be pruned yearly to remove all growth except new one-year-old fruiting canes and renewal spurs.
Grapes are produced from buds that will grow into shoots on one-year old canes. The most fruitful canes will be those that were exposed to light during the growing season. These are thicker than a pencil in width and as close to the trunk as possible (when cane pruned), explained Strik.
To cane prune, select two to four new fruiting canes per vine. Cut back each of these to leave about 15 buds per cane. For wine grapes, leave about 20 to 30 buds per plant. In table grapes, leave 50 to 80 buds per plant. Leave a one-or two-bud spur cane near the fruiting cane with one or two buds each. These "renewal spurs" will produce the fruiting canes for the following year and thus maintain fruiting close to the trunk. All other cane growth should be pruned off.
Most table grapes produce the highest yield of good quality fruit when cane-pruned.
To spur prune, prune along main canes to leave two- to three- bud spurs, each four to six inches apart. Leave no more than 20 to 80 buds per plant, depending on the type of grape. Remove all other one-year-old wood.
For more information, see Growing Grapes in Your Home Garden (PDF - EC 1305), or call 1-800-561-6719 to purchase a printed copy.