Having seen some spectacular vines, I'm always anxious to see another. In my own garden, I'm trying to keep two of these wonderful plants alive in very alkaline, clay soil (something they don't like). I dream that one day I might have these vines with pendulous blossoms covering arbors in my garden.
Wisteria is one of several members of its genus that are popular ornamentals. Wisteria belongs to the Fabaceae (pea or bean) family and can climb trees and shrubs up to 65 feet high. The white-bark vines, which always twine clockwise around their host, can grow up to 15 inches thick.The fragrant flowers, one-half to three-quarter inches long, come in purple, blue-purple, lilac-blue or white. They bloom in pendulous clusters 8 to 20 inches long, usually in April and May. (The flowers last longer if protected from the wind.) The colorful blossoms set against the gray bark make an attractive addition to any garden.
There are 12 species of wisteria, two of which are native to the United States (the others are native to Asia). Wisteria floribunda is the Japanese wisteria, Wisteria chinensis is Chinese wisteria and Wisteria venusta is silky wisteria.
All cultivated wisteria are similar in height, leaf and flower structure. Japanese wisteria has more fragrant flowers than the others. Chinese wisteria has shorter flower clusters, but they all open at once. Chinese wisteria is also the most shade-tolerant species. A silky wisteria has heavy, short flower clusters, and the leaflets have long silky hairs.
Japanese wisteria was introduced to the United States around 1830 and is hardy enough to grow in most areas of Utah.
Wisteria vines prefer to grow in full sun, but established vines will grow and flower in partial shade. They often climb surrounding vegetation to get sunlight. The vines sometimes resemble boa constrictors as they curl around poles or plants. But be careful when planting wisteria, because twining vines can strangle trees or other plants.
In fact, there is a wisteria vine in Sierra Madre, Calif., that is touted by the Guinness Book of World Records as the world's largest blooming plant. It was planted in 1894 from a one-gallon pot and now covers one acre and weighs 250 tons. It produces 1 1/2 million blossoms during its five-week blooming period.
Wisterias need a sturdy support such as an arbor, pergola or strong fence. The vines grow rampantly and eventually pull supports if they are sturdy enough. If you allow wisteria to grow on your house, provide a trellis or other support. Keep the vine from getting under the siding or from climbing down spouts or hanging on gutters.
Set new plants a foot away from the support and tie the young branches to the support to start them growing in the right direction. Keep the plant well watered the first year. Add mulch around the base to keep the roots from drying out.
The plants can also be trained to a single trunk. Remove all but one stem and stake this to a stout support. When the trunk reaches its desired height, pinch the vine to force branching at the head. Pinch long shoots back to further encourage a tree form. Remove all the buds or sprouts from the main trunk.
Wisterias tolerate a variety of soil and moisture conditions but prefer loamy, deep and well-drained soil. Heavy clay and alkaline soils often tie up the iron, causing leaves to lose their color or turn yellow.
Pruning established wisteria vines can be confusing. Wisterias bloom on 1-year-old growth. If you prune away previous years' growth in the spring, the flower buds for the current year are also pruned away.
Prune the vines twice a year: In the spring, remove dead, diseased or damaged branches and shoots that grow in the wrong direction just before the plant begins to leaf out. Do not cut back into 2-year-old wood, as this causes rampant vegetative growth that may interfere with flowering.
After the vines have flowered, remove half of each long new stem. The following spring, prune each shoot back to two to five buds. These buds will produce the large pendulous flowers.
The most common question I get is, "Why won't my wisteria bloom?" Although this isn't always the case, it is generally because the plant is in a juvenile or vegetative state.
Be patient! It often takes seven years for vines to mature enough to produce consistent blooms. If a wisteria does not bloom, it might not be receiving enough light, or it might be getting too much nitrogen fertilizer.
Sometimes root pruning stimulates flowering. To prune the roots, push a spade or shovel into the ground in a circle around the plant. Make the circle one foot away from the trunk for each inch of trunk diameter.
Avoid adding extra nitrogen fertilizer to the soil. You can add extra phosphate fertilizer, but avoid applying too much because phosphorous can tie up iron in the soil and make plants chlorotic.