In warm climates, where the winter temperature rarely dips below freezing, grape vines require no special winter protection. However, if you're trying to grow grapes in Minnesota or Maine, you'll need to winterize the grape vines to protect them against the biting cold and heavy snow. Grow cold hardy varieties of grapes to have a better chance of success. Beta, Kay Gray, St. Croix, Valiant or Worden are all juice or table grapes to consider. Wine grapes tend to be more sensitive to cold, but the University of Minnesota Extension Office says that Foch, St. Pepin, Edelweiss and Elvira grapes can be grown in cold climates with adequate winter protection.
Prune your grapes each year so that the plant is a single trunk that can easily be removed from its trellis. Normally, grape vines are pruned to have several "arms" that permanently attach themselves to a trellis, but in cold regions you'll need to cover the vine in winter, so you'll want to trim it to be easy to work with. Pruning is typically done when a grape plant is dormant, usually in late autumn.
Detach the grape vine from the trellis at the end of the growing season, after all the leaves have fallen off the plant. Cut back any new shoots to within a few inches of the trunk, but make sure there are one or two buds left at each base. Don't worry if you need to cut the vine back severely. Fruit is produced on new wood, so heavy pruning will encourage a better harvest.
Lay the vine flat along the ground.
Cover the vine with at least six to eight inches of soil or mulch, such as dried leaves, straw or shredded bark. Check on the grape vines several times before the snow fall to make sure that the mulch isn't displaced. In very cold locations you may need a thicker layer of mulch.
Uncover the vine once the ground is workable. Depending on your local weather, this will probably be around mid April.
Tie the trunk onto the trellis. As new growth forms, train the shoots to grow straight up so that they will be easier to prune back later.