How to Grow and Care for Japanese Wisteria

Japanese wisteria is native to a range that is located in a temperate location. It will thrive in areas that are similar to its native habitat being cold tolerant, but it’s also sensitive to extreme heat. Its USDA zones are 4-9.

Japanese wisteria

Wisteria floribunda (Willd.) DC.
Pea family (Fabaceae)

Background
Japanese wisteria was introduced to the U.S. in 1830. It has been widely planted and cultivated and is still very popular in the nursery trade despite its weedy and destructive habits. It is probably frequently misidentified as Chinese wisteria.

Distribution and Habitat
Japanese wisteria is found invasive in the mid-Atlantic and southeastern U.S., from New York to Florida and west to Texas. Wisteria prefers full sun, but established vines will persist and reproduce in partial shade. Vines climb trees, shrubs and manmade structures. It is tolerant of a variety of soil and moisture regimes but prefers deep, loamy, well drained soils. Infestations are commonly found along forest edges, roadsides, ditches, and rights-of-way.

Ecological Threat
The hard woody vines twine tightly around host tree trunks and branches and cut through bark, causing death by girdling. On the ground, new vines germinating from seed or sprouting from rootstocks form dense thickets that smother and shade out native vegetation and impede natural plant community development. As girdled trees die, canopy gaps are created which increase the amount of sunlight reaching the forest floor. While this may temporarily favor some native species, it also stimulates vigorous growth and further spread of wisteria.

Description and Biology

• Plant: deciduous woody, twining vine that climbs upwards in a counter-clockwise direction; stems are slender, brown and densely hairy when young, becoming hairless with age; older plants can grow to 15 in. or more in diameter.
• Leaves: alternate, compound, 8-12 in. long, with 13-17 (11-19) leaflets; leaflets egg-shaped with wavy-margins and strongly tapering tips.
• Flowers, fruits and seeds: flowering occurs in April before the leaves expand; flowers are violet to violet blue, occur in pendulous racemes 1-3 ft. in length and open sequentially from the base to the tip; flowers are 0.6-0.7 in. long on 0.6-0.8 in. long stalks (pedicels); fruits are velvety pods 4½-7½ in. long, broader towards the tip, and contain 3-6 round, flattened seeds each about ½ in. in diameter; pods begin to appear soon after flowering, mature during the summer and may persist for quite a while on the vines.
• Spreads: by seed which, in riparian areas, is transported by water; vegetatively by producing stolons (above-ground stems) that produce shoots and roots at short intervals.
• Look-alikes: Chinese wisteria; American wisteria (Wisteria frutescens) with leaves 7-12 in. long, 9-15 leaflets of uniform size, margins plane, tips acute to slightly tapering, smooth bright green above, undersides slightly milky; flowers in May after leaf expansion, flower clusters 4-6 in. long and not especially pendulous, individual flowers about ¾ in. long, pale lilac-purple with a yellow spot; fruit green and glabrous (not hairy); seeds swollen, bean to kidney-shaped; and trumpet creeper (Campsis radicans) with opposite, compound leaves, leaflet margins toothed, flowers red-orange, tubular and bloom late spring through summer.

Prevention and Control
For small infestations, cut vines to relieve trees of the weight and girdling; treat cut stems with a systemic herbicide containing glyphosate or triclopyr; new plants will grow from seed; long term management is needed (see Control Options).

How to Grow and Care for Japanese Wisteria

Les Engles achieved Master Gardener through the Camden County Extension of the Rutgers Master Gardeners Program. He is an arboretum curator with over 30 years of experience. He describes himself as a “tree-hugging dirt worshipper” who is a member of multiple gardening societies and foundations.

Julie Thompson-Adolf is a Master Gardener and author with over 30 years of experience in year-round organic gardening; seed starting, growing heirlooms, and sustainable farming.

Japanese Wisteria (Wisteria floribunda) is beautiful climbing vine known to grace arbors and trellises all over the country. Its smells delightful and its colors and blooms dazzle the eyes. But without proper care or placement it can become destructive and a real headache for you and your community.

Of the many wisterias used in landscape design today Chinese wisteria (Wisteria sinensis), Japanese wisteria (Wisteria floribunda), and American wisteria (Wisteria frutescens) are the most common. Japanese Wisteria floribunda was brought to the United States in the early 19th century for ornamental use and has since become invasive in many parts of the country. Before thinking of planting Japanese wisteria, check with local ordinances to see its invasive status.

Light

It is important to plant Japanese wisteria in full sun or partial shade to ensure it produces its full number of blooms. (Full sun is considered six hours of sunlight a day.) While this sounds easy, the climbing growth habit of the plant makes this more complex with wisteria. Wisteria likes to climb over structures that often create shade. Creating a structure, like an arbor or a pergola, rather than letting wisteria climb on a house that creates shade will negate this issue and create a new focal point in your yard. Additionally, wisteria vines can cause damage to houses, so don’t allow it to climb buildings.

Soil

Wisteria will tolerate various soil conditions as long as they are well-draining and consistently moist but not wet. Wisteria will not do well in wet areas. It prefers an area with loamy soil that is loose and organically rich. When considering pH levels, it is not tolerant of alkaline or very acidic conditions. It prefers a range of 6.0 to 7.0 pH.

Water

Like most trees and shrubs, wisteria only needs regular watering during their first year. They will benefit from regular watering to help establish their roots. After this first season, wisteria should only need supplementary watering during dry periods. When watering plants, remember long deep watering that is infrequent is better than quick, frequent watering.

Temperature and Humidity

Japanese wisteria is native to a range that is located in a temperate location. It will thrive in areas that are similar to its native habitat being cold tolerant, but it’s also sensitive to extreme heat. Its USDA zones are 4-9.

Fertilizer

Less is more when it comes to fertilizer and Japanese wisteria. If planning to fertilize, do so with a low nitrogen fertilizer (N in the NPK ratio). Fertilizing your plant only once a year or every other year, or even not at all, is acceptable.

If your wisteria is not blooming, you may be over-fertilizing with nitrogen. You can shock the plant into bloom by stopping fertilizing and root pruning. To root prune, use a shovel to cut the roots in a circle about two feet away from the plant’s trunk. Doing this will stress the plant and may force it into bloom.

However, it pays to be patient. Wisteria may take about three years to bloom, so don’t be discouraged if your new plant doesn’t put on an impressive show right away. Prune properly, and soon you’ll enjoy brilliant blooms. Also avoid planting seed-grown wisteria, which can take up to 15 years to bloom. Instead, look for grafted varieties or well-established plants.

Pruning

Japanese wisteria flowers bloom on new growth, so you will need to prune twice a year to manage both size and to keep branches close to the main structure to allow for enjoyment of the profuse blossoms. Doing this is an easy task and is done by pruning new growth back to six inches in July or after the wisteria has flowered. This is a really great time to do maintenance pruning and remove any growth not needed for the main structure of the plant and prune away suckers. During the winter or second pruning you will want to remove at least half or the prior seasons growth, remembering that wisteria only blooms on new wood.