Garden Variety: The right way to prune grapevines

Just like the informal communication system, the grapevines growing in your backyard can get a little unruly if left to their own devices.

To keep the plant version in check and encourage good fruit production, vines really need to be pruned heavily each year. The best time to perform this task is late winter, so dig out the garden gloves and head out to the garden sometime over the next several weeks.

The bad news about grapevine pruning is that it can get complicated quickly. Even experienced gardeners may balk at learning the finite difference between the single-curtain, four-cane kniffin, high cordon and other training systems. Guides will also refer to cordons, fruiting spurs, renewal spurs and various formulas of how to calculate the number of buds to leave per plant.

To keep grapevines in check and encourage good fruit production, they need to be pruned heavily each year.

Rather than allowing yourself to get overwhelmed, keep the basics in mind and remember that in most cases poor pruning is still better than neglecting the plants completely. You can and should remove 80 to 90 percent of the vines each year (once plants are established) to maintain fruit production. Left unpruned, vines become weak and spindly, fruit will be smaller and ripen unevenly as it is shaded by excessive leaves, and disease-causing fungi build up in the old plant material. But you can grow grapes successfully without a scientific following of the four-cane kniffin system.

Basic tips are outlined below. For detailed information, consult K-State Research and Extension’s guide “Grapes,” The Ohio State University Extension Fact Sheet “Basic Principles of Pruning Backyard Grapevines,” or a similar guide.

To prune grapevines growing on a fence, trellis, wall, arbor or similar structure, prune the center structure of the plant to look like a fan. The main trunk should be short and stocky, with four to six similarly-sized canes growing off it in a fan shape.

On each of these canes, prune back everything growing from them to leave only short pieces of cane, called spurs. Each spur should have two to four buds. Fruit and new canes will grow from these spurs. To summarize, you will be left with a short trunk and four to six upright canes. Each upright cane will have several short spurs. Everything else can be composted.

To prune grapevines growing on a single or multiple wire trellis, the main trunk should reach all the way to the top wire. From it, leave two long canes (cordons), with one growing in each direction along the wire.

Clip each of the canes growing from these two long ones to leave short spurs in the same manner described above. You will basically be left with a T-shape, with several short spurs along the top of the T. Again, everything else can be composted.

For both methods, try to eliminate spurs left from previous years and old wood, leaving the youngest, healthiest pieces of vine to produce the new year’s crop.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation. She is the host of “The Garden Show” and has been a gardener since childhood. Send your gardening questions and feedback to features@ljworld.com.