Wisteria: A Vine For The Ages

In a few weeks, some lucky locals with south-facing walls — planted with a magnificent, but occasionally finicky, woody vine — will be blessed with incredible flowers.

Hanging like long, blue and occasionally white pendants, wisteria will flower throughout the Hamptons for weeks — well into late May and early June. They can be tough to get started, but once established, they tend to even outlast the buildings they grow upon.

These wonderful vines evoke images of exotic Asian gardens, pergolas covered with their pendulous flowers and old stately houses with the vines tenuously twining up supports, spreading this way and that. Drives through the countryside can also turn up these sentinels of bygone estates and gardens, as the tendrils give clues to the long-ago landscape. You can spot a few of these along Sunrise Highway heading west and 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 others, 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 spring and early summer — 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, or Fabaceae, home to nearly 20,000 species of trees, shrubs, vines, and herbs. The genus — named in honor of Caspar Wistar, who was an anatomy professor at the University of Pennsylvania — includes 10 species of deciduous climbing vines. Two are native to the South and the rest hail from eastern Asia.

In fact, when wisteria was first discovered in the early 18th-century American colonies and shipped back to England, it was believed to be a pea plant based on its pods and bean-like seeds. 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 no additional nitrogen in the form of fertilizer because it creates its own. This is one of the areas where gardeners get into trouble with wisteria, since nitrogen fertilizer seems to stall or completely halt flowering, even after the plant has matured and is of a flowering age.

Wisteria has vigorous, twining vines with wide landscape usage where space permits, or where gardeners are committed to keeping them in bounds — which 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, upward of 65 feet. They are greatly valued for their large, pendulous flower clusters that bloom in the spring and seem to drip and cascade in flowering profusion when they are happy. They 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). Ah, but which way do our native wisterias twine?

Wisteria sinensis, or Chinese wisteria, and Wisteria floribunda, or Japanese wisteria, are typically grown in our Northeast gardens — the former the most popular of the two, due to its flowering habit, though its sprawling nature can be an issue. It grows up to 25 feet tall, or higher, and its flower clusters are 6 inches to 1 foot long.

Individual flowers in the clusters, which are violet-blue and slightly fragrant, open all at once for a very showy display starting in May, but a vine growing against a south-facing wall, or light-colored building with southern exposure, may bloom as early as April. A white-flowering form of Chinese wisteria — W. sinensis “Alba” — is very fragrant, while “Black Dragon” has double, dark purple flowers and “Plena” has double, rosette-shaped lilac flowers.

Wisteria frutescens is one of our native American wisterias, which you find mostly in the South, though it is hardy in southern New York, too. Some cultivars do quite well out here, as long as they have moist soil. They are not as tall as the Asian varieties and the flowers not as scented, and have smooth seed pods, as opposed to a velvety covering. Wisteria macrostachya, or Kentucky wisteria, is very similar to W. frutescens, with some subtle differences — most notably, it is non-invasive and begins to flower in just three years.

Older, established plants may have twisted, woody trunks several inches in diameter. Even though they are hollow, gnarled and split, they are tenacious and continue to offer flowering shoots year after year. But 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 cheap wisteria plants, they are probably from seed grown W. chinensis and the type you should avoid. However, plants that are grafted, 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).

In order to bloom well on the East End, all wisteria require full sun — six or more hours of direct sunlight per day — and a deep, moderately fertile, moist soil that does not dry out excessively. They will adapt to most soils, though they prefer neutral to slightly acidic, with a pH of 6.0 to 7.0 for best results. As mature vines become woody and quite heavy, they will need some type of support, and if you are growing them near a structure, like a house, be sure to keep them 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, needs correction. Prepare the soil in a 2-to-3-foot-wide area that’s 18 to 24 inches deep. Mix the native soil with either compost, peat moss with added humus, or well-rotted manure, one third by volume, to improve soil aeration and drainage. Being a legume, these plants are not fond of having their roots disturbed, so be careful when transplanting any potted plants.

More on this wonderful plant next week — and it’s not too early to ask at your local garden center what varieties they’ll be getting in. Maybe reserve one that strikes your fancy and might work in your landscape.

And in the meantime, keep growing.