The best time to prune grapevines in Iowa is late winter or early spring. Pruning can start in late February and should end by early April. Grapevines pruned during this time frame may bleed heavily. However, this bleeding of sap will not cause harm the vines.

The main reason for pruning grapevines is to control the quality and the amount of grapes produced. A grapevine produces grapes from buds that will grow into shoots on 1-year old canes (the long stems that have produced fruit for at least one year). Cutting back the number of fruit clusters produced will encourage energy to those remaining to be larger and more uniform, as a single grapevine can produce 200-300 buds.

Most home grape growers don’t prune their vines enough. When gardeners prune a neglected vine, they should remove the majority of wood previously produced. Vines that are two-years and older are not fruitful. Usually, the most fruitful canes are thicker than a pencil and grow near the main trunk.

There are two basic methods used to prune grapes – cane pruning or spur pruning. Cane pruning is commonly used for Concord and other American varieties, and best suited to vines whose canes are most fruitful at a considerable distance from the base.

Spur pruning is a more successful method for most French hybrids since most of these varieties bear their most fruitful buds near the base of the canes. On these vines, all wood is spur-pruned to one to five buds for fruit production, or cut back to shorter spurs (one or two buds) for renewal growth.

Did you know? For further information on pruning grapes, visit the ISU viticulture website found at: www.extension.iastate.edu/viticulture/.

Horticulture Questions? Contact McCormick at yvonne@iastate.edu for information or advice.