Wisteria Mysteria

Wisteria is a wonderful vine that evokes images of exotic Asian gardens, pergolas covered with its pendulous flowers and stately old houses with the vines tenuously twining up supports as they spread this way and that. Drives through the countryside can also turn up these sentinels of long-gone homes, estates and gardens as the tendrils give clues to the long-ago landscape, and you can spot a few of these along Route 27 and along the northern end of the Hutchinson River Parkway in Westchester.In some settings the vines seem to be a disarray of quickly encroaching green and in some settings they are carefully pruned to shape and form.  At times they are even shaped to look like shrubs, grown as a tree-like standard" or treated in a bonsai effect. But the plant is generally misunderstood, improperly cared for and it’s been known to frustrate many a seasoned gardener who may wait years or even decades  for that first wonderful flower that signals late spring and early summer. And all this to say nothing of its fall colors, gnarly trunks and shoots that are displayed all winter long in their nakedness.

Wisteria is a member of the pea family, Fabaceae (formerly Leguminoseae). The genus was named in honor of an anatomy professor at the University of Pennsylvania, Caspar Wistar (1761-1818). The genus includes 10 species of deciduous climbing vines, two native to the southern United States and the others native to eastern Asia. In fact, when it was first discovered in the Colonies in the early 18th century and shipped back to England it was believed to be a pea plant based on its pods and bean-like seeds. And indeed, they are closely related … as gardeners should remember before they go to pour on the fertilizer … which, after establishment, is generally unnecessary. Being a legume, this plant needs little to no additional nitrogen in the form of fertilizer because it creates it own. This is one of the areas where gardeners get into trouble with wisteria, because giving it nitrogen fertilizer seems to stall or completely halt flowering even after the plant has matured and is of a flowering age.

Wisteria are vigorous, twining vines with wide landscape usage where space permits or where gardeners are committed to keeping them in bounds. And keeping them in bounds can mean pruning once or twice a year. But prune them at the wrong time and, again, you stall or eliminate flowering. Among their attributes are hardiness, vigor, longevity and the ability to climb high … at times to 65 feet. They are greatly valued for their large, pendulous flower clusters that occur in the spring, and they seem to drip and cascade in flowering profusion when they are happy.  The flowers are pea-like and may be white, pink, lilac-blue, bluish-purple or purple in color, and several years ago I was delighted to discover a rare bi-color on a Depression-era estate. The fruit is a long, green flattened and often hairy pod that is not particularly ornamental. The plant climbs by means of twining stems and has alternate, pinnately compound leaves. And as a matter of fact some believe they can identify the particular species by observing if the vines twine clockwise (Japanese) or counterclockwise (Chinese).

Older, established plants may have twisted, woody trunks several inches in diameter. Much to the dismay of many a gardener, plants that have been grown from seed remain in a long juvenile stage and often don’t bloom for 10 to 15 years or longer. This is generally true of the Chinese variety and if you find really cheap (as in bargain catalogs) wisteria plants they are probably from seed grown W. chinensis and the type you may want to avoid. However, plants that are grafted, and plants grown from cuttings or layered from a flowering plant, will usually begin flowering years earlier than seedlings. So a word to the wise … know the sexual origin of your wisteria (hint, grafted would be asexual).

Two species of wisteria are typically grown in our northern gardens: Wisteria sinensis or Chinese wisteria, and Wisteria floribunda or Japanese wisteria. The Chinese wisteria is the more popular plant due to its flowering habit. It grows to a height of 25 feet or more and has flower clusters 6 inches to a foot in length, which open before the foliage has expanded. Individual flowers in the clusters open all at once for a very showy display. Flowers are violet-blue and slightly fragrant. Plants are most showy from early to mid-May in most seasons but a vine growing against a white or light-colored building or wall with a southern exposure may flower as early as late April.

There is also a white flowering form of Chinese wisteria, W. sinensis "Alba," which is very fragrant. Two cultivars include: "Black Dragon," which has double dark-purple flowers, and "Plena" with double, rosette-shaped, lilac flowers. Chinese wisteria may bloom within three to four years after planting; however, the juvenile period may be much longer.

Wisteria frutescens is one of our native American wisterias and one you find mostly in the South. However, it is hardy in southern New York and you can find some cultivars that may do quite well out here, though it prefers a moist soil. It is not as tall as the Asian varieties, and the flowers are not as scented and the seed pods are smooth as opposed to the velvety covering that the Asians have. Wisteria macrostachya (Kentucky wisteria) is very similar to W. frutescens with some subtle differences, and it’s notable because it begins to flower in only three years.

Japanese wisteria grows to a height of 25 feet or more and has violet-blue, fragrant flowers that bloom as the foliage is also expanding. Individual flowers open gradually from the base of the cluster to the tip. Clusters can be 12 to 18 inches in length and are at peak bloom in late May in most years. The plant has yellow fall foliage color. There are numerous cultivars of Japanese wisteria with various flower colors. A few include:

Alba—white flowers

Carnea—"flesh"-pink flowers

Longissima—light-purple flowers, clusters very long

Longissima Alba—white flowers, clusters 15 inches long

Macrobotrys—reddish-violet to violet flowers, clusters to 3 feet or longer

Praecox—more dwarf, blue-purple flowers

Purpurea—purple flowers

Rosea—pale rose, tipped purple, 18 inches long

Rubra—deep pink to red flowers

Violacea Plena—reddish-violet flowers, double

In order to bloom well in this area  all wisteria require full sun (six or more hours of direct sun per day) and a deep, moderately fertile, moist soil that does not dry out excessively. They will adapt to most soils, though they prefer a neutral to slightly acid soil pH of 6.0-7.0 for best results. Some type of support will be necessary, as mature plants can be quite heavy, and if you are growing them near a structure, like a house, they will need additional support and to be kept away from gutters and downspouts.

Good site preparation will help ensure plant establishment. Begin with a soil test to determine if the soil pH or the phosphorus level need correction. If so, make additions of materials as you are preparing the soil. Prepare the soil in an area two to three feet in diameter and 18 to 24 inches deep. Mix into the native soil either peat moss with added humus , compost or well rotted manure, one-third by volume, to improve soil aeration and drainage.

More on this wonderful plant next week, but in the meantime, keep growing.

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