Overgrown grape vines are usually characterised by a maze of twining and climbing vines as well as canes crossing and recrossing themselves. The tentacle-like vines won't flower and fruit very well if the plant must support overgrown vegetation. To maintain an unruly grape vine, you'll spend some cold winter days outdoors, giving your grape vine a hard prune while it's dormant. This means cutting the old vines off and allowing only the main trunk, with new-growth buds or nodes, to remain. If your grape vines don't have support, such as a training wire or trellis, you'll need to install support as part of your maintenance effort.
Wait until grape vines are dormant but no longer frozen to begin maintaining your overgrown grape vine. This is usually early winter in warm-weather regions and late winter in cold-weather areas.
Find the grape vine trunk. This is the thickest and oldest part of the vine protruding from the ground. For heavily tangled vines, locate the trunk by selecting one rope-like section and severing it. Follow its path back to its source. If the vine does not lead to a trunk, rake it up and discard it.
Keep selecting, severing and discarding runaway vines until you have located the trunk, or main vine stem. Use a sharp bow saw to cut the trunk back to a height of about 6 inches. Leave two growth nodes on the trunk. These will grow into new fruiting vines.
Follow the same procedure to locate and hard prune other trunks. Even among overgrowth tangled with brush and weeds, you'll know other trunks are in the area if you see other grape vines climbing up nearby trees or along the ground.
Place a wooden support about 4 feet high behind the stem or trunk if one is not there already. Secure the grape vine trunk with twine to the post.
Walk off a distance of about 8 feet on either side of the support. Dig holes 2 feet deep. Insert 8-foot-high wooden posts into the holes. Close the holes and tamp down soil until posts are secure. About 2 feet of post should be underground, leaving about 6 feet of post above-ground.
Insert screw hooks into each post to secure wire or training twine that will hold the new fruiting canes that grow from the grapevine trunk. Place the first set of hooks about 3 feet above the ground. Place the second set of hooks at about the 5-foot point.
Run wire or twine between the posts. Pull taut and secure with staples. Wrap excess wire or twine around itself to provide extra support.
Train the two new canes to grow along the lower wire by wrapping the young canes around the wire or twine as they grow. Clip off any other canes that have grown out from the trunk. Allow the trunk to continue to grow upward to the top wire.
Continue maintenance efforts every year. In year two, select the two strongest new canes at the trunk top and train them to run along the top wire. Remove the weaker new growth. Each subsequent year, prune away about 90 per cent of new growth to enable grapevine to maintain its structure, leaving a few new buds to grow until vine is mature and productive.
You can speed up spring growth by adding mulch around the grape vine trunk base. When warmer spring weather arrives, remove the mulch to let the sun warm the soil. Replace it in midsummer to retain moisture. When your grape vine trunk reaches the second wire or the top of your trellis, clip it off at that point to retain the vine's height. Every year, clip off any new vines or canes that grow from the trunk-top.
Always wait until plants are dormant to prune them, no matter how vigorous seasonal growth is.