Pruning grapes is not a fine art as they are tough little cookies, but they are more productive and less unruly with correct pruning and training. Harvesting becomes easier, grapes are fewer but are larger, there's less problems with diseases plus they ripen faster.
Let’s start at the beginning when you first bring a grape plant home. Although it is maybe tempting to give it a good haircut, don’t. It is important for the plant establish a good framework and a good root system before any trimming takes place.
Grape plants are woody vines and need a support such as a fence, arbor or horizontal post system. I have mine growing along a 6 foot fence and it works quite well. I initially used a thin gauge wire to train the vining stems, however, this proved inadequate. In just a couple of years, the wires sagged and broke under the weight of the fruit laden stems. Arbors are another alternative and evoke images of a Mediterranean garden as the grape clusters dangle down from a leafy canopy. Pruning and securing the plant is more arduous though as you need a ladder to maintain it.
An efficient grape support is a wire trellis. To make one, sink sturdy posts into the ground 10 feet apart with intermediate posts every two feet. The posts should be 5 feet above the ground. Run one 9 gauge wire horizontally between the posts a couple of feet apart at the top. Add another one about 2 feet above the ground if you wish to another level for the vines to grow upon.
The first pruning should be done in winter. This is to establish a basic framework. Select the sturdiest stem that is growing more or less upright to become the main trunk. Tie it to the main support. Once the main stem reaches the top wire, cut it back to two strong buds. Those buds will become the 'arms' reaching in opposite directions along the wire. As the buds develop into stems, tie them to the wire as they grow. If you have a two wire system, look for two strong stems that arise closest to the lower wire and tie them to their support.
As the 'arms' grow, new shoots will grow along their stems. These new stems will grow with gusto producing many grape clusters. If they are not cut back, the grapevine will become a monster and the grape clusters will be many but the grapes themselves will be small. To increase the size of the grapes and to control its growth,cut back any side shoots to a couple of buds (nodes) on each of those side stems.
If your grape plant is more mature, and it needs remedial pruning, determine which stem is your main upright trunk and which are its ‘arms’. Select the most vigorous stems. Remove all other growth; just keep the main trunk and the horizontal arms. Tie them to their support if they are not secure. Cut back all the side branches emerging from the arms to 2 to 4 buds. These buds should develop into fruiting spurs, where the grapes will develop. Once all the side shoots are cut back to a 2 to 4 buds, thin the side shoots so they are about 10 to 12 inches apart.
When it comes to training a grape vine on an arbor, pergola or other overhead structure, plant at least one on each side of the structure. That is all you need if the structure is small, however for larger ones, consider planting one at each support post or every other one depending on the distance between the posts. Prune the winter after planting. Cut back the main stems to just beyond where you want the plant to branch out, about 2 feet off the ground. Remove all the remaining side shoots. When the main trunk starts to branch out, select the most robust ones and tie them to their support. For remedial pruning and training for older grape vines, select the healthiest main stems. Keep one or two main stems on each plant and tie them to their support (or just twine the vines around their support). Remove all the side shoots of the main stems to a 2 to 4 buds (nodes). If any of the main stems are long enough, guide them over top the trellis and secure.
There are numerous methods of pruning grape plants, but this method is not too complicated and it works. More on pruning grapes as the season progresses.
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