If you are wondering how to prune grapevines, you are not alone. While some vines can be left alone and require no pruning, this is not the case with grapevines. Left unpruned, a grapevine quickly becomes a tangled mess with runaway shoots and diminished fruit production. Fortunately, pruning doesn't take a lot of time, and will keep your grapes looking neat and tidy as they produce a bumper crop of fruit.
When to Prune
In the first two years, most pruning takes place while the plant is actively growing, to encourage new shoot development in desirable locations and discourage it along the trunk of the vine.
Prune mature growth while the plant is dormant, usually late winter or very early spring is best. Warmer climates have less of a window of opportunity, and pruning usually needs to be completed before mid-February. Cooler climates have more time to work with, but pruning should still be complete before the plant shows any sign of new growth.
The pruning tool you use should be the one that is most able to make a clean cut in the vine. A clean cut is less stressful to the plant, and creates less exposed surface area that could provide entrance to disease-causing organisms. For the same reason, keep your pruning tools scrupulously clean and, if you are pruning a large number of plants, clean your tool occasionally as you work to prevent cross-contamination in case one of your vines is diseased.
Choose your pruning tools based on the thickness of the wood you are cutting. Choose simple hand pruners for cutting one year old wood, but you may need to use a saw or lopper for older growth.
How to Prune Grapevines Each Year
Grapevines generally need three years of growth before they begin to bear fruit. Each year of development requires a unique approach to pruning for optimum plant health and fruit development.
First Year Pruning
In the first year, you are working to encourage growth along the length of the vine and prevent bushiness. For this reason, cut all lateral shoots that form from the vine. Whenever possible, avoid cutting leaves as they are necessary for the plant to harvest energy for growth. If the vine reaches the top of the trellis or arbor, pinch of the tip of the vine and allow two lateral shoots to spread out in either direction at the top of the support structure.
Second Year Pruning
This year of growth, the vine will probably reach the top of the support structure. At this time, you need to pinch the end and train two lateral shoots to climb along the structure as described above. If last year's lateral vines have begun to form lateral shoots along the top of the support, allow these to grow but trim off any lateral shoots that grow from the trunk of the vine.
When the two main lateral shoots have grown as far as you want them on the support, pinch off the ends to encourage tertiary shoots to fill out the rest of the available space.
Woody canes from the previous year can be trimmed back at this time as well. Cut each cane back to either a renewal spur, characterized by a single node, or a fruiting spur with multiple nodes.
Third Year Pruning
Perform third year pruning, and all pruning thereafter, in late winter when the plant is dormant. Cut one-year-old wood back to multi-noded fruiting spurs, with each spur evenly spaced and pointing downward. As a general rule of thumb, the Ohio State University fact sheet advises that you should aim aim to prune 80 to 90 percent of year-old wood, and leave 40 to 50 fruiting nodes each year.
Pruning Mature Plants
Fruit only forms on the current year's growth, and an overabundance of mature wood will discourage new vegetative growth. Each year, continue to prune away most of the mature wood as you did on the third year pruning to encourage new shoot development and good fruit production.
Pruning Grapes Becomes Instinctual
Learning how to prune grapevines takes time and experience. In time, you will develop an instinct for how much you need to take away and which nodes you need to leave to create the most vigorous grapevines. With a little patience, your hard work and practice will be rewarded with an abundance of sweet, flavorful grapes.