Wisteria

Wisteria plants originally grow in China, Korea, Japan and C. and S. USA, on trees, with the roots embedded in the forest floor in the rich organic matter of the leaf litter created by autumn leaf falls. The top growth of the plants grows strongly up ward to reach the light. Wisteria can displace native vegetation and kill trees and shrubs by girdling them. They have the ability to change the structure of a forest by killing trees and altering the light availability to the forest floor. Avoid planting wisteria near young trees as the vines may overgrow and strangle them.

There are 10 species of wisteria but three types of them are well known: Chinese wisteria vines (Wisteria sinensis), Japanese wisteria vines (Wisteria floribunda) and American wisteria vines (Wisteria frutescens).
Wisteria is a very vigorous, deciduous twining climber that find its perfect sites on walls, trellises, arbors, trees and pergolas. Wisteria can also be grown as a single trunk standard or a tree-form. Stems are large with smooth, tight gray to white bark, twining anticlockwise around the support. Alternate, pinnate, dark green leaves are tapered at the tip with wavy edges. Lavender, pink or white hanging chain of flowers are fragrant, very showy and abundant, and appear in spring or early summer. Seed are in a flattened bean-like pod.

Even fully hardy plants, they need protection from wind, as their flower buds are sometimes destroyed by late frosts. It is best to provide them with a southern or western exposure and to allow adequate space. Avoid east-facing walls because the early sun will exacerbate damage to frosted flower buds. The heavy vines last for many years, so provide a sturdy support. Wisterias do not transplant well and usually suffer a severe setback if moved. Large specimens sometimes do not recover so try to find the best place for this plant form the very beginning.

Wisteria need full sun and a fertile, moist soil that does not dry out excessively, well-drained, if possible enriched with peat moss, leaf mold, compost or well rotted manure. They will adapt to most types of soils, though they prefer a neutral to slightly acid soil with a pH of 6.0-7.0 for best results. Plant them in spring, placing each one at 25 to 30 cm apart from its support. Place the root ball of the plant in the hole so it is no deeper than it originally grew in the nursery. If your wisteria is grafted, set it so the graft union is slightly below the soil surface. Fill in the hole with the prepared soil mix and firm it around the root ball. Water well after planting, soaking the entire area.

Young plants should be tied to the support until the branches are thick enough to support themselves. Feed the vines every spring with a balanced fertilizer. Gardeners in northern zones will need to provide a mulch for winter protection.
Pruning in late summer will help to contain the growth and encourage flowering so cut back the leafy sideshoots to 5-6 buds from the main stem. Repeat the pruning again in winter shortening them to 2-3 buds. Wisteria can be trained to a tree form by staking and pruning severely for many years, until the trunk becomes thickened.

You can propagate wisteria by layering or from stem cuttings. Take basal cuttings from sideshoots in early to midsummer and root with bottom heat. Layer in autumn or graft in winter. You can also propagate it by sowing its seeds but plants that have been grown from seeds will remain in a long juvenile stage and often do not bloom for 10 to 15 years or longer. Plants that are grafted or grown from cuttings or layered from a flowering plant will usually begin flowering earlier than seedlings.