One of the most critical -- and confusing -- aspects of growing grapes is when, how and how much to prune them. Cut away too little and the plant becomes a rampant monster; cut too much, and yields of any fruit is greatly reduced. Timing is similarly important, and while grapes can be snipped back any time during the plant’s dormancy in winter, later is generally better.
1. Growing Grapes
With more than 5,000 strains of grapes to choose from, a vine exists for virtually every yard. All fall into one of two types: American grapes (Vitis labrusca), which are the hardier and more disease resistant of the two, usually growing in U.S. Department of Agriculture plant hardiness zones 4 through 9; and European strains (Vitis vinifera), which are typically hardy in USDA zones 6 through 9. Hybrids have varying hardiness. Vines usually do not produce viable crops of any size until the fourth year after planting and then only with careful training and pruning of the canes.
2. Timing for Pruning Grapes
Most growers wait to prune their grapes until late winter or early spring, after the deepest freezes have passed but before the weather has warmed enough to goad the vine into breaking dormancy. Pruning in the fall or before the vine has entered dormancy causes the plant to generate new growth, which not only draws strength away from the roots but which will be killed off by impending frost. Early pruning also reduces the grape’s vigor over its lifetime. Pruning during freezing weather is generally not harmful to grapes, but delaying pruning until late winter may delay bud break in the spring, which increases bud survival if there is a surprise late spring frost.
3. Effects of Pruning
Unless the goal is to grow a dense, leafy grapevine over an arbor for shade, pruning is critical for an abundant crop of fruit. Grapes only produce fruit on the new growth from the previous year, and fruit yield is diminished on an unpruned plant. Pruning of young plants should be with the aim of establishing a strong permanent trunk and vigorous root system; older plants should be pruned to select strong fruiting canes from year to year. Keeping the shoots pruned back relatively close to the trunk causes the vine to concentrate its energy into the fruit clusters that form.
4. Pruning Goals
In the first year, the emphasis should be on training one or two strong leaders to an upright support and allowing the plant to establish a strong root system. In the second year, the vine should be headed back -- or the top cut off -- when it grows taller than its support, to promote strong trunk and lateral cane growth. Remove any lower side shoots or suckers as they appear from the base. In the third year and beyond, prune back old growth in late winter as well as last year’s growth to several strong buds. These buds will produce the current year’s fruit crop. Make pruning cuts between the buds, with at least an inch of cane left on the vine past the terminal bud. Vines should be heavily pruned, with about 90 percent of the previous year’s growth removed at each annual trim.