Pruning Your Grapes

Grape plants are the next thing to weeds; you have to be intentional to kill them. My first contact with a “disease” some farmers call “tractor blight” came as I was trying to learn how to hold a straight line as I disced. I took a couple of two-year-old vines off at ground level. Distraught, I sought the advice of another farmer who laughed and told me to wait.  Within a week or two there were new canes growing up out of the ground…no harm done.  So, remember, no matter how much you think you are butchering the vine, it will survive.

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.

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. Grapes are very susceptible to powdery mildew, so foliage needs to be thinned. 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. Don’t take too much or you can sunburn the fruit. If you end up with mildew, use sulfur.

Grapes are very versatile. You can eat them as a snack, in salads, dry them as raisins or make wine. It has been grown as a crop for thousands of years. If you have questions that are grape-related, UCCE Master Gardeners in Tuolumne County will be available for questions at Open Garden Day on March 2. The demonstration garden is located on Barretta Street in Sonora at “the Dome.” The garden opens at 10:00 am; demonstrations start at 10:30.

Jim Bliss is a University of California Cooperative Extension Master Gardener of Tuolumne County.