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Get to know wisteria before planting it

KENNEWICK -- Wisteria is a beautiful, woody vine that intertwines over and around structures, creating a romantic, picturesque garden tableau.

I've always been an admirer of this vine, but there are some complexities that gardeners may encounter when growing wisteria.

Differences between Japanese, Chinese wisteria species

There is more than one species of wisteria. The two most common ones are Chinese wisteria (Wisteria sinensis) and Japanese wisteria (Wisteria floribunda), native respectively to China and Japan.

The Chinese wisteria tends to be favored by gardeners because its showy flowers open all at once before the leaves develop. Its fragrant flowers range in color from violet to blue, purple, lilac, rose, pink or white.

The Japanese wisteria's fragrant flowers open more gradually, starting at the base of the cluster with blooms beginning at the same time the leaves are starting to grow. There are numerous named cultivars with different flower colors from purple to violet, red-violet, rose, pink, ivory and white.

Both wisteria are hardy for our area, but Japanese wisteria blooms about two weeks earlier and wraps itself around structures in a clockwise direction. The Chinese wisteria climbs in a counterclockwise direction.

Wisteria that don't bloom

Wisteria are hardy, fast-growing, woody vines. While they prefer a moist, rich, slightly alkaline soil, they will tolerate more challenging conditions. It's true that wisteria grow like weeds.

In fact, they have become invasive in 19 eastern U.S. states, vining upward, girdling and killing native forest trees.

Wisteria are easy to grow, but many gardeners complain that their vines aren't flowering. That can be a problem. Vines will only start to flower when they reach the mature stage. It can take a vine started from seed more than 10 years to grow out of its juvenile state. That's a long time to wait for flowers, even for the most patient gardener. For earlier flowering vines, plant vines started from cuttings or grafted onto rootstocks. Lack of flowering also can be attributed to too much fertilizer, heavy or improper pruning, winter injury to flower buds, or too much shade.

Support structures begin to crack

Another complaint about wisteria is that it devours the structures to which it has been trained to for support. Considering that wisteria vines can live 50 years or more when given the proper care, it's not surprising that this long-lived vine often outlasts garden structures.

Good planning can help avoid problems that result when the wisteria start to crush and crumble the arbor, pergola or porch column to which they've become entwined.

I would recommend against growing them close to or on part of your house. Wisteria vines are known for getting underneath siding and roofing and into gutters. It's safest to grow them on arbors, pergolas and wire trellises away from the house.

The most durable structures of heavy metal pipe set in concrete work best, but gardeners often prefer wooden structures for aesthetic reasons.

Use beams of pressure-treated or rot-resistant wood if you want your structure and vine to last. Bases should be set firmly in concrete. Whatever you use for support, remember these vines get big and heavy.

Pretty but poisonous

It's important to note that wisteria flowers are followed by brown 4- to 6-inch seed pods in the fall.

All parts of the plant are considered poisonous, but especially the seeds. They contain a particular glycoside -- wistarine -- which causes severe gastroenteritis when ingested. Children and small animals can be poisoned with just one to two seeds.

The wisteria is a pretty vine, but get to know its complex nature before you decide to plant it.

* Marianne C. Ophardt is a horticulturist for the Washington State University Benton County Extension Office.

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