When to Prune Grapevines in California

Goals of Pruning

• Grapevines are identified as woody tree climbers, or lianas. They climb by twining or by attaching their tendrils to supporting structures. Pruning maintains the same structure and plant shape each year to facilitate cultural care and harvesting. Pruning regulates the number of branches and buds on each branch. This concentrates growth, which improves grape quality. Pruning also improves bud fruitfulness.

Summer Trimming

• Grapevines grown in California gardens are sometimes pruned in the summer rather than late fall or winter. Home grapevines may be grown for their decorative look on a backyard patio or arbor. These vines grow 10 feet or more each year, and a summer trimming is necessary to manage growth. Grapevine shoots and canes that are shortened to 4 to 6 feet still produce abundant grape harvests. In hot inland California valleys, the vines should not be pruned to expose grape clusters to the intense sun.

Overgrown Grapevines

• An overgrown grapevine in any of California's climate regions may be pruned in winter. Begin the process by cutting out all dead or diseased wood and wood with dark, crackled bark. Well-spaced, strong 1-year-old canes are then chosen to remain as the plant's structure. The rest of the canes are removed. The following year, in the dormant season, all but the strongest several vines are removed and re-trained onto the support system.

Selecting Canes

• The quality of canes chosen to remove or retain is an important part of the pruning process. Quality of individual canes is more important than quantity of canes in producing a good harvest. Medium diameter, round, well-browned canes with buds 3 to 3 1/2 inches apart produce the best-quality grapes. The buds should be plump. Avoid choosing flattened canes of poor color, with long internodes. Canes that have been exposed to sunlight are more productive the following year than those that developed in the shade.