Tips And Tricks For Pruning Grape Vines

Learning how to grow your own grapes at home can be an exciting endeavor, but maximizing your yield and maintaining healthy plants depends heavily on when you prune. Grapes sit squarely on the list of plants you shouldn't prune in the fall, but mature and established vines should be pruned yearly during winter after all leaves have dropped. A good pruning time frame is between December and March. 

As Oregon State University Extension Service horticulturist Erica Chernoh explains, "Home grape growers don't prune their vines enough. When gardeners prune, they should remove the majority of wood produced the previous season—until about 90% is pruned off." This allows the grapevine to focus its energy on maturing only the fruit clusters it can handle. An unpruned vine can produce too many grapes, also known as overbearing, resulting in fruit that is low quality and takes longer to ripen.

Before pruning, it's important to know some terminology associated with grapes. The trunk anchors the plant to the ground, while the head is the spot at the top where the trunk puts on new growth (also known as the renewal zone). A cordon is a branch that comes out of the trunk and is trained along a wire. New spring growth is referred to as shoots but then "becomes a cane after the growing season," according to Oregon State University. Located on the cordon or the head, a spur is a cane that has been pruned to retain one to five buds.

There are two main methods of pruning. The first is called cane pruning, which involves cutting back the plant to two lateral canes that emanate from a central trunk. The head of the trunk is called the renewal zone. Select two canes that emerged this year, are no thinner than a pencil, and already have several buds along their length. Everything older should be removed, as grapes only produce fruit on one-year-old branches. Using clean loppers, cut back all but these two canes, which can be bent and tied to grow where desired. You should also leave two older shoots coming out of the head of the vine, trimming them down to their second bud if you live in a warmer climate. 

For grapevines with cordons — extensions of the trunk grown laterally — there is a different technique known as spur pruning. This may sound familiar if you also have fruit trees that don't have much room to grow, as it is similar to espalier-style growing patterns. Cut back growth so all that remains are one to two bud spurs on each arm along the cordons. Next year's vines will grow from these spurs. For areas with multiple canes clustered together, keep the healthiest one and take it down to just one or two spurs. If all look the same, keep the cane closest to the cordon. Trimmings can be dropped onto the compost pile, mulched, or even rooted to propagate new plants.

There are some summertime pruning practices that will help grapevines stay healthy and productive. First, if you failed to prune enough over the winter, there is somewhat of a grace period early in the season when you can prune back anything you missed. This is also the right time to thin out excess shoots that have sprung up, effectively maintaining just one shoot per node. If unsure of which to keep and which to eliminate, it's a good idea to retain the longest shoot and trim back the others. Fruit thinning is the technique for removing the clusters from any shoots that are shorter than three feet so that only the longest (and thus strongest) shoots will put on fruit. Likewise, you'll also want to pare back how many clusters are growing on each vine. For young vines, keep just one cluster per vine, with any extras clipped off before the plant begins to set fruit.

Another summer practice that will promote the health and vigor of your grapevine is leaf pulling. This is essentially what it sounds like: the practice of removing leaves during the growing season to ensure that adequate sunlight will reach the fruit. While grapes are about the size of a pea, look to remove leaves from the side of the plant that receives morning sun; removing leaves from the side that gets afternoon sun could lead to sunburned grapes.