Grape Pruning
Grapes are grown for many reasons: ornamental, shade arbors, fruit and wine. All of them share one thing in common: grape plants are the next thing to weeds; you have to be intentional to kill them. In the wild, a single vine can cover an acre and can pull down trees and bushes.
Winter, when grape vines are dormant, is a great time to plan for pruning. From late fall through early February, rain and wind carry microbes that can enter grapevines through pruning cuts and eventually kill the vines. In March, when grape buds begin to swell in the lower elevations, is an ideal time to prune grapes after the danger of killing frost is past. Choose a dry day with no rain in the forecast for the next couple days in order to avoid those rain-carried microbes.
Pruning for an arbor or fence top is easy, just trim to taste. Vines prefer to produce foliage, so the berries will likely be small.
Grape clusters grow on shoots from buds that formed the previous year. For best fruit production, you need to remove up to 90 percent of the previous year’s growth, but you also want to leave some buds on each vine. The question is, which ones?
For fruit you need to prune severely—a method called cane pruning. Tie a cane to the stake the first year and then top it just above a bud below the wire. Canes will emerge from this junction. Anything below is a sucker and needs to be pulled off while still green. (If you cut it off, you leave behind a large number of buds which will continue to send out shoots.) After the summer’s growth, and after the vines are dormant, a number of canes originate from the head. Only first year’s growth will produce next year’s fruit. Prune other canes back to the head. First year canes will be smooth and not have true bark on them. Leave from two to four canes on each side of the head and tie them to the horizontal wire.
Wine grapes are cordon, or spur, pruned (cordon means arm in French). The first year, tie two canes to a horizontal wire, one going in each direction. All other canes should be pulled off (they are suckers). After the first year when the arms are established, all canes are pruned from the arms leaving behind a spur with two or three buds on it. Each spur produces canes for foliage and grapes for wine.
Another thing to keep in mind is summer pruning. Prevent canes from dragging on the ground. Prune all of them about a foot above ground level to provide air circulation. You may also need to thin the overhead canopy a little for the same reason.
For more information, refer to: UC Sacramento Master Gardeners: in the Vineyard
Jim Bliss is a is a UCCE Master Gardener of Tuolumne County.
