Q: I’m stumped by what to do with some badly neglected grapevines that came with our new home. Their supports are long gone, and they have been sprawling all over the ground for years in what I actually thought was a twig pile. I know the vines should be pruned, but I have no idea where to begin. — Kim Neumann, Erie, Colo.
A: Prune boldly, without fear of hurting a thing. No need to worry over which vines should go and which should be saved. Cut all the way back to the main trunk, a gnarly thing only about 2 to 4 feet long. (It might be growing straight up, but more likely it’s now leaning over, perhaps all the way to the ground.) In the spring, dozens of new shoots will grow out along this trunk. You should rub or snap off most of those, too, saving only about three with which to start the structure of your new grapevine. (Next winter the best of the three will be the one to keep.)
After you’ve cleared the jumble away from the main trunk, it’s time to begin work on building an arbor or trellis to support the vine. Finish construction before new shoots sprout in the spring. The mature vines are wiry and tough, but young shoots are surprisingly brittle and easily snapped off by the wind unless they have support. Make the arbor strong enough to hold not only the vines, leaves, and fruit, but also several hundred pounds of ice and snow that may cling to the vines in winter.
As you ponder what sort of an arbor or trellis to build, it’s good to know a little more about how grapes grow and how much pruning they typically need every year (a lot). The simplest system involves a row of posts with a strong wire fastened along the top—a great way to train them if you just want fruit. But grapevines can take practically any shape you like: Adjust the height of your new trunk to match that of your trellis, and make as many arms off that as you need to cover the space you wish to fill, to maximize fruit, or to create a shady bower.
On a typical commercial wire trellis, individual plants are spaced at least 8 feet apart along the row, and the perennial trunks grow up the posts. The vines (usually called canes) grow horizontally along the top wire, one extending in each direction. Think of each plant in this system as having a T shape. (It’s a pretty messy T: A number of sprouts will develop at its top, and each arm will have several drooping side branches.) Thus you can create a hedge of greenery or a canopy over a dining area, or even cover a wall.
Each spring, both arms of the T are renewed completely. Last year’s canes that bore fruit are cut off, and two of the biggest new shoots at the top of the T are tied to the wire to replace them. The rest of the new shoots at the top are removed. (The fruit grows on side shoots that sprout from the two main canes; fruit forms only on new growth, never on old wood.) In nature, grapes grow up into trees and sprawl all over the canopy. Gardeners tend to prune them too lightly. You could use a chain saw at ground level, and sprouts would still shoot up from the roots, so don’t be intimidated. Hack yours back to the trunk—and get busy on that trellis.