According to Bernadine Strik, a berry crops professor at Oregon State University, "Home grape growers don't prune their vines enough." The appropriate pruning and training of grapevines is essential to producing a bountiful fruit harvest. If not done properly, grapevines produce too much foliage and vegetation, instead of fruit, and they become unruly and difficult to deal with.
It is essential to choose the type of training and pruning system you will use for your grapevines while they are young--1 to 2 years old--otherwise, the vines may be tangled and have too much foliage to work with easily. Choosing the type of training for your grapevines also helps you know which method to use for pruning each year.
The high cordon, or cane-trained, pruning system is good for home gardeners, because it is not too difficult to establish and maintain. Plus, it is an easy way to create attractive landscaping with your grapes, such as having them grow on an arbor.
You should prune grapevines in winter months--generally, January through March for most regions--and you may need to remove as much as 90 percent of the previous season's growth each year.
Choose two shoots to be the top trunks while the grapevine is young. Secure them to a wire or arbor--one in each direction, like small arms reaching out. Tie them with cloth or bread ties, so they stay in place.
Select 1-year-old growth--canes that developed in last year's growing season--as fruit wood or vegetation wood. Vegetation wood is where next year's shoots will grow to produce fruiting wood.
Trim the fruiting wood canes down to three to five evenly spaced nodes, and trim the foliage wood down to one node. Trim in a manner that allows remaining vines to trail downward from the two primary trunk arms at the top.
How much pruning you do depends on how much vegetation was produced the previous year, but, generally, young grapevines need 85 to 90 percent of growth cut off. This aggressive pruning helps the vine keep its shape, produce better-quality fruit and distribute the load of growing fruit more evenly along the vines.
Once your grapevine has matured to at least 3 years of age, prune back until you have about 40 to 50 buds left.