Grapes are grown for many reasons: ornamental, shade arbors, fruit and wine. Each of these purposes requires a different approach to pruning. All of them share one thing in common: 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 arbor or fence top is easy, just trim to taste. You will most likely not get a lot of fruit and the berries will be small.
For fruit, you need to severely prune your vine. This method is called cane pruning. You train the vine to a head at the top of your stake next to the wire. To do this, you tie a cane to the stake the first year and then top it just above a bud below the wire. Canes that emerge from this junction are what you want. Anything below is a sucker and needs to be pulled off while still green. Only the first year’s growth will produce fruit for the next year. First year canes will be smooth and not have a true bark on them. Leave from two to four canes on each side of the head and tie them to the wire.
Wine grapes are cordon pruned (cordon means arm in French). To do this, take two canes the first year and tie them to the wire. After the first year when the arms are established, all the canes are pruned from the arms leaving behind a spur with two or three buds on it. It is from these spurs that you will get your grapes (referred to as spur pruning).
These three methods cover the way most vines are pruned, but each varietal has its own method. For example, zinfandel should be cane pruned, not spur pruned. Look up the varietal you want to grow to make sure of the pruning style that will give you the best yield. Another thing to keep in mind is summer pruning. Grapes are very susceptible to powdery mildew, so the foliage needs to be thinned. Keep the 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. They have been grown as a crop for thousands of years. Master Gardeners will be demonstrating grape pruning at Open Garden Day on March 4 at the Demonstration Garden at 251 S. Barretta Street, Sonora, from 10:30 to 1:00. If you have any questions that are garden- or grape-related, call the University of California Master Gardeners hotline at (209) 533-5912 or email us at email@example.com.
Jim Bliss is a University of California Cooperative Extension Master Gardener of Tuolumne County.