Wisteria is best known for its pea-like blossoms in varying shades of white, rose and lavender. Once established, wisteria is not difficult to maintain. It will survive with average rainfall, and bloom with little to no fertilizer. However, wisteria does need seasonal pruning to ensure spring blooms and compact growing. Otherwise, you could end up with 25 feet of rambling vines and no flowers.
Wisteria is native to the United States, as well as, eastern Asia. The Chinese and Japanese cultivars are most commonly used in landscaping since their blooms are fragrant, unlike the US varieties. Regardless of the variety you choose, follow these guidelines for years of prolific blooms.
Wisteria come from seed or has been grafted with a cutting off of a mature plant. Wisteria that come from a seed will take up to 15 years to bloom, but wisteria that has been grafted will bloom within four years. Most nurseries only carry wisteria that has been grafted, but be sure to ask about the plant’s origin, especially if the price is low.
Chinese wisteria, also called Wisteria sinensis, is the most popular variety. Before its foliage emerges, Chinese wisteria blooms in one huge display during mid-spring in white or varying shades of purple, depending on the cultivar. Their bloom clusters reach 6 to 12 inches long, while the vines can grow up to 25 feet if left unchecked.
Japanese wisteria, known as Wisteria floribunda, has a longer bloom cycle than its Chinese relative, flowering while its foliage emerges. It also comes in more colors ranging from rose, white and violet-blue. Japanese wisteria has longer bloom clusters, ranging in size from 12 to 18 inches. It will also reach heights of 25 feet or more.
Choosing a site
In order to bloom, wisteria needs full sun and moist soil. It prefers slightly acidic soil, but they will adapt to most soil conditions. Wisteria is a vigorous vine, so you will need to build support for your plant. Most ready-made trellis will be pulled apart by your wisteria. Also, avoid using your house or other building structures as support, since the vines are capable of ripping off shingles and siding.
Supporting the vines
Trellises or pergolas can be made out of pressure treated wood or galvanized wire. Wisteria can easily pull apart nails, so bolt your materials together. As part of your yearly maintenance, retighten bolts that have been worked loose by the vines. You can also grow your wisteria on a live tree, but check it regularly to be sure the wisteria does not completely encircle the tree with one of its vines, cutting off nutrients and water.
Planting your wisteria
Prepare the planting site by digging a hole 2 feet wide and 2 feet deep. Mix in organic material and manure with the soil to retain moisture and provide nutrients.
Place the wisteria root ball so it is slightly below soil level. If your plant is grafted, place the graft union about an inch below ground level. Cover the roots with the mixture of organic material, manure, and soil. Water the plant well.
Wisteria sinensis alba
New plants should be watered weekly so they will establish their root systems. Also, annually add a nitrogen rich fertilizer until the plant fills the desired space. At this point, you should encourage foliage and vines rather than blooms. Once your wisteria has reached its desired height, stop fertilizing to promote development of buds.
After your wisteria has established itself, it will need pruning on a seasonal basis. When your wisteria plant first begins to branch out in the spring, pick the main leader vines that you wish to encourage. A good rule of thumb is to pick one vine per board on your trellis or arbor, then remove all other vines. Once your leader vine has reached the end of the trellis, pinch it off at the end to encourage side growth.
During the summer, side shoots will develop off of the main leader vines. Trim shoots back to the sixth or seventh leaf so growth will be limited for the season. As a result of your pruning, new side shoots will appear that will need to be removed as soon as they begin to leaf.
When early winter arrives, cut back the main leader vines to 1/3 to 1/2 their length, and trim side shoots to 2 inches from the base. This method of pruning will maintain the shape and size of your wisteria plant while encouraging blooms. Left unpruned, wisteria vines can grow up to 10 feet in a single growing season.
Lack of blooms
A wisteria’s lack of blooms could be caused be a couple of issues. First, determine if your plant came from seed or was grafted. Wisteria started from a seed will take up to 15 years to bloom. Next, make sure the growing conditions are right for your plant. Wisteria needs at least six hours of full sun to develop buds. If your plant does not have full sun, you may try to moving a young plant. However, once established, wisteria does not transplant well.
Also, look to see if your plant is receiving too much nitrogen through excess organic material or improper fertilizer. If your wisteria has an abundance of foliage without blooms, you will need to use a high phosphate, no nitrogen fertilizer. Lack of or improper pruning can also discourage blooms. Severe winters can also damage buds, diminishing the following spring’s blooms.
Disease and pests of wisteria
Wisterias are especially resistant to diseases and pests. If you find disease or pest damage, take a damage portion of the plant to your local nursery or extension office for diagnosis.
By establishing your plant and pruning seasonally, you will be rewarded with years of extravagant wisteria blooms.