Wisteria Vine

Culture Notes
A fast-growing vine that can reach 30 feet or more and stretch for more than a hundred feet, wisteria is usually trained to a trellis, arbor or other more confined structure but any support must be of sturdy construction as the plant will become extremely heavy in time. Plants can topple structures and trees. The vine is invasive and has taken over the edges of woodlands in many regions of the US. Plant it with caution!

Consider planting the native wisterias including American Wisteria, W. frutescens, (zone 5, southeastern US into Florida in coastal wetlands to dry mountain tops) and Kentucky wisteria, W. macrostachys (Illinois to Louisiana). They are far less aggressive that Asian species.Flower displays on the natives are spectacular, but not quite up to the drama of the aggressive Asian species. Flowering is on new growth so winter pruning is suitable. Spring flowers come in violet to white. W. frutescens 'Amethyst Falls' flowers when young, sometimes in one-gallon containers, is a repeat bloomer, grows slower than 'Nivea', and about one-tenth as slow as the Asian wisterias. Late spring to summer flowers of W. macrostachys appear as those of American wisteria are fading. W. macrostachys is cold hardy well north into Minnesota. W. macrostachys cultivars include 'Clara Mack' (creamy white flowers), 'Aunt Dee' and 'Blue Moon'. The native wisterias will be better where terminals can be seen from the top or side of the plant.

The main ornamental feature is the drooping clusters of violet flowers borne in the spring.  The flower color can vary depending on the cultivar used.  The plant will adapt to most soil pH levels, but prefers full sun for best flower production.  The seeds are poisonous. This plant grows so fast that root pruning might be a good method to control rampant growth. Be prepared to control growth in some fashion. Stems root as they touch the ground helping them spread quickly. Humans have been poisoned by eating seeds.

Pruning is needed to keep this aggressive vine contained.  The vine can be seen when it is in flower in many urban areas where it has escaped its original bounds in a nearby yard.  It is probably best used for training to grow onto an arbor where flowers can droop forming a showy, fragrant ceiling of color. Be sure the arbor is strong enough to support this aggressive vine. Most flowers are produced in older growth so any pruning should be done after flowering. It can be maintained as a shrub in a landscape with plenty of room provided it is pruned several times during the growing season.  Old plants can be cut to the ground to basically start over. Avoid excessive applications of nitrogen fertilizer as these lead to foliage growth to the detriment of flowering.  No fertilizer is needed in many situations.

Planting and establishing shrubs

The most common cause of young plant failure is planting too deep.  Plant the root ball no deeper than it was in the nursery.  In most instances, the root flare zone (point where the top-most root in the root ball originates from the trunk) should be located just above the landscape soil surface. Sometimes plants come from the nursery with soil over the root flare. If there is soil over this area, scrape it off.  The planting hole should be at least twice the width of the root ball, preferably wider.  In all but exceptional circumstances where the soil is very poor, there is no need to incorporate anything into the backfill soil except the loosened soil that came out of the planting hole.  Never place ANY soil over the root ball. If a row or grouping of plants is to be installed, excavating or loosening the soil in the entire bed and incorporating organic matter enhances root growth and establishment rate.

Weed suppression during establishment is essential.  Apply a 3-inch thick layer of mulch around the plant to help control weed growth.  Keep it at least 10 inches from the trunk.  If you apply it over the root ball, apply only a one or two inch layer.   This allows rainwater and air to easily enter the root ball and keeps the trunk dry.  Placing mulch against the trunk or applying too thick a layer above the root ball can kill the plant by oxygen starvation, death of bark, stem and root diseases, prevention of hardening off for winter, vole and other rodent damage to the trunk, keeping soil too wet, or repelling water.  Regular irrigation through the first growing season after planting encourages rapid root growth, which is essential for quick plant establishment.

Pests, Diseases and Damaging Agents
Pests:  Black vine weevil may attack wisteria.

Diseases: Crown gall causes formation of galls on the main roots or stems. Leaf spots may be seen, but infected leaves can be picked off.  Powdery mildew coats the leaves with a white, powdery growth.