Wisteria is one of the most beautiful, but rambunctious, vines planted in Nantucket gardens. Its pendulous flowers are a show stopper when they cascade from the leafless branches in late spring or early summer. But Wisteria has well-warranted reputation as a garden thug. Judicious pruning is essential in maintaining this vine.
Before beginning, it’s helpful to keep your objectives in mind: To remove dead or damaged wood; to remove excessive vegetative growth; to tie in young branches to fill areas that need coverage; to stimulate flower production close to the main framework.
Follow these steps to prune an established Wisteria while dormant:
1) Take a good look at the underlying structure of the vine. While pruning, its important to maintain a strong framework, so that when flowers form, they are evenly spaced all over the pergola or trellis that the vine is growing on.
2) Remove all lateral growth sprouting from the trunk that is not a part of the main framework. If grown on a pergola, the trunk is often maintained completely bare, with no lateral growth allowed to mature. These spindly stems will run along the ground, and root quickly. If any have already taken root, be sure to pull them up. The goal is to cultivate the upper portion of the vine that has been grafted onto the rootstock. Any growth that sprouts from below the swelling on the trunk where the graft was made will likely never flower, or even have the same characteristics as the scion.
3) Cut back young lateral branches, leaving only three or four buds. If there are bare areas of the support structure, tie in well placed laterals while pruning systematically across the canopy. Don’t hesitate to tip short spurs that were naturally formed during previous seasons. This method of pruning forces energy directly into the remaining few buds, causing them to form larger flowers that are held on short, strong spurs. The buds on the long, whippy growth from the previous season are not capable of producing flowers and will only form a tangled mass in the canopy of the vine. This makes it very difficult to do summer pruning later.