Question: When and how do I prune my grapes? — H.P.
Answer: Fall has arrived and thoughts turn to pruning plants in the landscape. Fall may not be the optimal time to prune certain plants. As for grapes, they should be pruned in early spring while still dormant before new growth begins.
If the vines have been neglected for years, attempt to prune the vine back to a single trunk. Select the new trunk from canes that are growing from the base of the vine and cut back to the desired height. Keep two lateral canes on each side of the trunk to produce fruit the current season. Determine the type of support to use, and tie these canes to the support (fence or trellis). If no lateral canes exist, wait until next year and select two new shoots to train into being the cordons. A cordon is a horizontal extension of the grapevine trunk. Any other old wood should be pruned and removed from the vine.
With a new planting of grape vines, determining how to prune them will be dependent upon available space and the type of training system used. Ideally, begin pruning during the first year to develop a straight trunk and strong root system. Prune the vine back to a single, straight cane. Tie this cane to a support to assist it with growing straight. Once new growth begins and the vine reaches the top of the support, remove 1 to 2 inches of the terminal growth to encourage the vine to branch out. Select two branches, growing in the opposite direction of each other, and tie to the support to train them to grow along the top of the support system. To manage the growth of the vine, remove any buds that may grow lower on the trunk.
After the first year, when the trunk has reached the desired height and laterals have formed, plan to prune each spring. Prune to allow for adequate air movement around the vines to reduce the incidence of disease. Keep in mind, heavy pruning results in high quality fruit production. Vines pruned lightly may produce abundantly, but the fruit is usually of poor quality. For wine varieties, it is recommended to have 20 to 30 buds per vine following pruning. With juice, jelly or table types, 40 to 60 buds per vine should remain after pruning. Grapes are produced on current season growth, which developed from the previous season’s wood.
Additional information on growing grapes in Wisconsin is available in publication A1656, Growing Grapes in Wisconsin, from the UW-Extension Learning Store. https://learningstore.uwex.edu/Assets/pdfs/A1656.pdf
Jeanne Hilinske-Christensen is the UW-Extension Interim Horticulture Educator for Kenosha and Racine counties. Submit plant care questions to the Master Gardeners Plant Health Advisers. Phone 262-857-1942 or email firstname.lastname@example.org.