American Wisteria

Size, growth and what to expect

American wisteria grows fast, nearly three feet a year in our growth estimator. It is a twining vine that climbs 15 to 30 feet, and one plant spreads 4 to 8 feet wide. Wisteria often waits 5 to 10 years after planting to bloom, and seed-grown vines can take longer.

Pea-like flowers, lilac to bluish purple and nearly an inch long, open from April into June in drooping clusters 2 to 6 inches long. A few more may follow in summer. Smooth pods 2 to 5 inches long ripen in late summer and split open in fall. Its leaves feed the caterpillars of the marine blue, the Zarucco duskywing, the long-tailed skipper and the silver-spotted skipper.

It grows wild from Virginia to Illinois and south to Florida and Texas. Its home is bottomland forests, swamps and the banks of streams and rivers. Planted vines have also gone wild in Connecticut, Massachusetts, Rhode Island, New York, New Jersey, Pennsylvania, Delaware, West Virginia and Iowa.

How to grow American Wisteria

American wisteria blooms best in full sun and grows in part shade, but not in full shade. It wants a moist, slightly acid soil rich in humus, and it takes ground that floods for a time. On limy soil its leaves can turn yellow. Shelter it from cold winds and from early morning sun on frosty mornings. Its twining stems grow heavy, so give it a strong support. It harms buildings less than the Asian wisterias do. Grown up into a small tree, it may damage the tree over time. Stand the support 4 feet from a wall, and set plants 6 feet apart. Keep it at least 15 feet from overhead wires.

Saplings ship potted. Wisteria dislikes being moved, and an established vine's large root system makes it hard to remove, so choose its spot with care. Plant it from fall to early spring, in a hole wider than the pot and no deeper. Set the crown at the soil line, put the native soil back in, and keep the mulch clear of the stems. Gather the pods in fall, before they burst, and let them finish ripening in an open tray. Soak the seed overnight, and nick its coat with a file to let water in. Sow it three quarters of an inch deep, and keep the soil moist until it sprouts.

Water weekly through the first summer and in dry spells until it is established. It fixes its own nitrogen, so feed it sparingly. Too much fertilizer grows leaves instead of flowers. It blooms on new growth. After it flowers, cut the long shoots back to about 6 inches, and shorten them again in winter to two or three buds.

Each flower carries both male and female parts, so there are no male and female plants to pair. Bumble bees and carpenter bees visit the flowers. Leaf spots, mites and leaf-chewing insects can show up, though none is serious. Eating any part of the plant can make a person sick, and the pods and seeds are the most poisonous.