Chinese wisteria (scientific name, Wisteria sinensis) is a deciduous perennial vine with a twining growth habit. It needs regular pruning to keep its growth under control and is regarded as an invasive species in many places. The plant's name is sometimes spelled wisataria, in keeping with the anatomist Casper Wistar, from whom the plant takes its name. Sierra Madre, California, holds an annual "Wistaria Festival" every March, during which visitors can view a vine that is 111 years old, weighs approximately 250 tons and bears over one million lavender blossoms.
Chinese wisteria, like all members of the wisteria group, is a stunning bloomer, bearing large, drooping clusters of fragrant flowers, usually bluish-purple, lavender, or mauve in color. Bloom time is usually mid-spring to early summer. A few kinds bear white blooms, such as silky wisteria (W. brachybotrys "Shiro-kapitan"). W. sinensis "Alba" also bears white flowers.
Chinese wisteria is a vigorous climber that can easily grow to 25 feet. Trellises and other supports must be very sturdy because the mature vines are very heavy and can break apart flimsy supports. The flowers are rabbit-proof (rabbits tend not to eat any part of the plant, in fact). This plant is deer-resistant, as well.
Chinese wisteria is part of the pea family, as evidenced by the velvety seed pods that appear after the flowers fade. The plant is native to parts of China and is generally hardy in USDA hardiness zones 5 to 8. Chinese wisteria can take up to 20 years to mature enough to produce flowers, but once it has matured, this plant is very long-lived; it can live up to 100 years.
Preferred Growing Conditions
Chinese wisteria, like its cousins, prefers well-drained soil that is made rich by adding compost. While many wisterias prefer lots of sun, Chinese wisteria has good shade tolerance, although the best flowering occurs only when it gets partial to full sun.
Because Chinese wisteria is such a vigorous grower, experts advise against letting them climb up a porch or the side of your house. Instead, let them grow on a garden arbor well away from the house. Such arbors, roofed by Chinese wisteria plants, are a perfect focal point for English cottage gardens.
Young plants can take many years to mature to the point where they bloom profusely, so you may want to shop for older (and more expensive) plants if quick blooms are desired.
Growing and Caring for Wisteria
Wisteria needs very little in the way of care, other than frequent and vigorous pruning to keep the vines under control. The plant will send out runners that can quickly overwhelm nearby structures. Feeding is usually unnecessary for this plant, but regular watering is recommended.
If you have trouble getting the vines to flower (this plant's most common care problem), there are a number of methods you can use to encourage flowering. You can begin by changing the fertilizer that you use (a high-phosphorus fertilizer may promote blooming). More importantly, change the way that you do your pruning. Heavy pruning tends to promote earlier and more prolific flowering.
To train wisteria vines, choose a single upright stem to attach to a vertical support, then religiously remove any side shoots as they appear, forcing the plant into upward growth. Pruned correctly, wisteria will form a beautiful overhead shade canopy. Once the plant reaches the height you want, vigorously trim the tips of the plant to stunt its further growth.
In much of North America, particularly on the east coast where conditions resemble that of the plant's native environment in China, Wisteria sinensis is listed among invasive plants. All parts of the plant contain a toxin known as wisterin that can cause vomiting and diarrhea; growers should be wary of pets and children eating the flowers or seed pods.
Two closely related species are the Japanese wisteria (Wisteria floribunda) and the American wisteria (Wisteria frutescens). Like Chinese wisteria, the Japanese species is known to be invasive, but its flowers are considerably more spectacular. It requires more sun than sinensis and is sometimes trained in Bonsai forms.
American wisteria is a smaller species, growing only two-thirds as long as the Chinese and Japanese forms. Although its flowers are less spectacular, the plants produce flowers at a younger age than Chinese or Japanese wisteria. The American variety is recommended for landscape use because it is much less invasive. American wisteria is found naturally in the southeastern US and in scattered areas including portions of Texas, Iowa, Michigan, and New York. American wisteria vines flower in lavender or mauve, and they will sometimes bloom again in September.
A subspecies, Kentucky wisteria (Wisteria frutescens var. macrostachya), is sometimes considered an entirely different species. Another native alternative for Americans is W. macrostachys ("Blue Moon" is a popular cultivar).