Wisteria is a woody perennial vine that can grow to the size of a tree if left to ramble. Wisteria is known for its pendulous purple flower clusters as well as for their lovely fragrance. It was popular in elegant Victorian gardens. Wisteria gives today's gardens the same touch of romance.
Wisteria has a downside, though. Because it is such a rampant grower, and because it twines around everything and anything in its path, it can become invasive. A vine planted too close to a building can do a great deal of structural damage if it is not kept properly pruned.
Wisteria is a legume, and a member of the Fabaceae family. Ten species are classified in the genus wisteria; two of the species are native to the southern US, and the other eight are native to Asia. The genus was named for Professor Caspar Wistar who was an anatomy professor at the University of Pennsylvannia around the turn of the 19th century.
Chinese wisteria, Wisteria sinensis, and Japanese wisteria, Wisteria floribunda, are the most popular types for home gardens. Both bear clusters of extremely fragrant flowers in spring about the time the leaves are opening. Flower clusters may be from six inches long to 18 inches long. Chinese wisteria flowers open at once, creating a beautiful display. Japanese wisteria flowers open over a period of two or three weeks, giving a more prolonged display.
Wisteria is an extremely hardy deciduous vine. Newly planted vines will not bloom for several years; this is their "juvenile" stage. When planting wisteria, plan ahead for its mature size. The main stem will become like a tree trunk, and the lateral vines will become extremely heavy and limb-like. A mature wisteria vine that uses a large tree as a support will often strangle the tree. A girdled tree that dies can be a hazard if it is near your home, especially if it is top-heavy with a large vine.
Wisteria climbs house siding, bricks, rain downspouts, other shrubs or trees. Anything the vine encounters, it will twine around. Once a vine has wandered under siding or roofing, it will continue to grow until it pushes the siding or roofing off the building.
A trellis may seem plenty sturdy when the vine is new, but within a couple of years, the tendrils and vining branches will be heavy enough to crush it. A better choice for supporting a new wisteria vine is a sturdy pergola. It should be constructed to last for decades, since wisteria vines are very long-lived.
Wisteria can also be trained using posts and strong wire. Plant the vine in front of a strong post. Secure the main stem up the post. Prune the laterals, allowing a few to grow in each direction along supported wires. Wisteria cultivated this way needs regular pruning to keep it within the bounds of the support.
An established wisteria vine that has rambled onto a building or onto a roof can be pruned back and re-trained. Remove all of the vines from the building, sawing off branches that are permanently growing in the wrong direction. Train the remaining branches to grow on a support away from the building. Keep new growth cut back along the building side, allowing the vine to wander in the opposite direction.
Pruning a wisteria vine encourages new growth. Heavy pruning when retraining wisteria will not harm a healthy vine.