Grape vines can quickly grow to 15 or 20 feet in length during their active summer growing season. Without a trellis or other support, you could end up with your grape vines all over your yard. A trellis will help keep your grape vines looking tidy and will keep the ripening fruit off the ground, where it becomes easy prey for hungry slugs, snails and other ground-dwelling creatures. You can prune during the summertime to help control your overgrown grape vine, but you'll want to do major pruning in fall, after you have harvested the grapes and the vines go into their dormant season.
Prune your grape vine with sturdy clippers in fall by cutting off up to 90 percent of all the vines, or canes. Cut all dead or damaged canes and leave only four canes on each side of the vine, which you will leave three to four feet long.
Build a trellis for your grape vine after you prune it in the fall. It's much easier to train the vines up a trellis when they first begin to grow in the spring than it is to attempt training long vines.
Prune your vine in the summertime if you must control the rampant, spreading growth of vines that are not supported. Using sharp clippers, cut off long vines mid way to the main trunk, avoiding grapes that might be forming, if possible.
Tie your rambling grape vines to a fence or sturdy nearby plant, such as a tree, if they get out of control in the summertime and you don't want to prune off any developing fruit. Pick up each individual vine and use green nursery tape to tie it to anything nearby that will support it.
Cut back grape vines with no main trunk or structure all the way to ground level in the fall or winter. If your grape vine has been grafted, cut it back six inches above the grafted area.