There are two basic methods of pruning grapes: spur pruning and cane pruning. The right method for your grapes is determined by whether your variety produces fruit only on long canes, or whether it can produce the fruit on short canes via spurs. If you know the variety of grape, you can just look up the recommended pruning method. If you don’t know, then I would suggest doing one half of the vine one way, and the other half the other way. The goal is to have more grapes, so whichever side produces best tells you the winning pruning method.
Both methods are done while the grape is in dormancy, before its buds start to swell and leaf out. In my area, I usually plan on doing it in late February. It can be done earlier, but if you have heavy rainfall, I would wait as long as possible, since the raindrops can spread disease, infecting the fresh cuts.
In this article, we will only be discussing spur pruning on an established grape vine, at least 4 years old. For younger vines, there is pruning to establish the main trunk and cordons, which I won’t be delving into.
Terminology: A grapevine consists of a main trunk, cordons, canes and shoots. The main trunk usually comes straight up out of the ground against some kind of support. It then branches into cordons, which come out at about 90 degrees from the main trunk. Depending on the method of chosen for growing the vine, there can be either one or multiple cordons coming off of each side of the trunk, each supported by wire or trellis, and are often about 2 feet apart, if multiple per side. From the cordons you will see canes coming off; these are last years’ shoots. These are what bore the grape clusters last year. I use shoots to name the fresh new growth that is soft and green, and canes to name these same shoots after the leaves fall and they turn woody.
In spur pruning, spurs are created by pruning the canes down to 2 buds. Most sources recommend having one spur every 6″, on average. This usually means that one cane gets entirely whacked and the other cane gets whacked back to two buds; this is if two buds from last years’ spur produced shoots.
This video, produced by Dave Wilson Nursery, shows Chuck Ingels illustrating how to spur prune: