Pruning grapevines is a specialized task sometimes called an "art" by those who are experts in this practice. Because grapevines grow quickly each summer season, they can reach 15 to 20 feet in length. All types of grapes need to be pruned in late fall or winter, after they produce their fruit, lose their leaves and become dormant. The vines of the grape plant are often referred to as canes, and you must prune as many as 90 percent of all canes to ensure a bountiful harvest the next summer or fall.
Pruning Grapevines the Right Way
Cut all diseased, unsightly or dead canes back to the main trunk of your grape vine after it has produced its fruit and lost its leaves. Make clean cuts with sharp clippers or loppers if they are too large for clippers---do not leave any ragged edges on your cuts.
Prune trellised grapes such as French Colombard and Chenin blanc into a "horizontal cordon" configuration. With this method of pruning, you leave two canes supported and tied on the plant's trellis and cut off all secondary canes to their connection point on the main trunk and on the permanent cordons on the trellis.
Prune in summer if your vines are unsupported by stakes or a trellis to keep forming fruit off the ground. If you prune in summer to control rampant growth, cut the longest canes halfway back to the trunk. When you make your cut, try to avoid cutting off small, forming grapes.
Prune grapevines that have no main trunk all the way back to the ground---perform this task in fall or winter when your vine is dormant.