The rolling hills of the wine country are lined with vineyards. In the summer, the green rows of grapevines (Vitis spp.) provide a beautiful contrast against the dry, brown hills. But when winter comes, the scene changes. The grapevines die back to shriveled brown vines, clinging to trellises while the ground is covered with green grass and mustard plants. In your garden, the grapevine growing over your arbor or fence follows a similar pattern, dying back in the winter until it appears completely dead.
As the days get shorter and colder, the grapevine loses its leaves and slips into winter dormancy. Like other deciduous plants, the green vines die back, leaving only dead vines and a woody trunk. The grapevine looks completely dead. In the spring, new vines will sprout from the trunk and spurs or canes grow rapidly through the summer into a tangled mass of vines and fruit.
Although grapes are grown across the United States, they grow well in mild Mediterranean-type climates. European varieties (Vitis vinifera) such as "Thompson Seedless" or "Flame Seedless," which grow in U.S. Department of Agriculture plant hardiness zones 7 through 9, or the native muscadine varieties (Vitis rotundifolia), which grow in USDA zones 7 through 10, may be damaged by extremely low temperatures or sudden freezes in the spring. In addition, a long, dry winter can desiccate and damage older grapevines and kill young plants.
Pruning is usually done in late winter or early spring, when the grapevine is dormant and before the new vines begin to sprout. You should remove up to 90 percent of last year's vines, leaving only a few short spurs or canes on the grapevine's woody trunk. New vines will sprout from the buds on the spurs and occasionally from the trunk. Remove any vines growing below the graft because they are growing from the rootstock and won't produce the same type of grape.
While grapevines are relatively hardy, a late freeze can damage the developing vines, blossoms and fruits. If a hard freeze is in the forecast, use stakes to surround the grapevine and cover the entire plant with plastic sheeting or tarps until all danger of frost has passed. Weigh down the edges of the plastic with rocks, bricks or boards. You can also place lamp rated for outdoor use under the plastic to add extra warmth, but be careful that the bulb doesn't touch the plastic and melt it. If the winter and spring have been unusually dry, watering the vines regularly will help stop the vines from drying out or dying.
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