It may seem counterintuitive to prune your Concord grapevine back to its bare bones during the winter, but heavy pruning is necessary for a higher fruit quality and production during the spring. Pruning removes the unproductive or dead arms from the stem and allows sunlight to reach new canes and promote renewed growth. Without proper pruning, the vine will produce an abundance of fruit that will be low in quality or unripened.
Plan on pruning your vine in late winter or early spring, depending on your location. You need to prune the vines before they come out of dormancy in spring, but not when there is a risk of a final spring freeze.
Separate your grape vines if there are two or more growing into each other. This will allow you to get a good look at each shoot to know which should be kept and which should be cut.
Cut off any arms with coarse or shedding bark. These arms are usually more than 2 years old and are no longer productive. Cut the arms at the fourth or fifth bud from the stem.
Look for yellowed or black vines. Cut into these at a bud with your pruning shears. If the inside of the vine is not green, the vine is dead and must be removed.
Remove any growth over the top of the vine support. This allows sunlight to reach any new growth.
Measure your canes (shoots that are 1 year old or less). Canes that are larger or smaller than a pencil's width should be removed. Make sure to leave at least 60 buds on your vine.
Tie your cane clippings together and weigh them. If the weight comes to one pound, the vine should be cut so that only 30 buds remain. For each additional pound, add 10 buds. For example, if your cane clippings weigh 2 pounds, leave 40 buds. This practice is called balanced pruning and is the best way to ensure a harvest with both quality and quantity.