Wisteria: American vs Asian Species, How to Grow It, and When It's Invasive

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At a glance

American vs. Chinese vs. Japanese wisteria

Wisteria is a genus of woody, twining vines in the legume family. Three groups are sold in the U.S., and the difference between them decides whether you are planting a garden vine or a future invasive problem.

The Asian-species details (earlier bloom on bare stems, longer clusters, leaflet counts, velvety pods) follow University of Maryland Extension; American wisteria's native range, smooth pods and rebloom follow NC State Extension. Both NC State Extension and the Lady Bird Johnson Wildflower Center list W. macrostachya and W. frutescens var. macrostachya as names for the same native species. UMD notes that out of bloom and without pods, Asian and American wisteria are hard to tell apart, and garden plants are often hybrids or mislabeled, so bloom timing relative to leaf-out and velvety (Asian) versus smooth (American) pods are the most reliable clues.

Is wisteria invasive?

Chinese and Japanese wisteria are. University of Maryland Extension states that Chinese, Japanese and hybrid Asian wisterias are invasive species: they escape into forest edges, roadsides and ditches, spread by seed and by stems running along the ground, and can kill mature trees by shading their foliage and strangling their trunks. All three are prohibited from sale under Maryland law. Master Gardeners of Northern Virginia reports them as invasive in forested areas throughout the Mid-Atlantic and Southeast. The North Carolina Forest Service fact sheet on Japanese and Chinese wisteria recommends removing them from commercial trade and planting native W. frutescens instead, and the Florida Museum notes that the two Asian species have escaped into natural areas and are regarded as invasive, while suggesting American wisteria as a Florida-friendly alternative.

Where these species are invasive, the responsible move is not to plant them, and to remove escaped vines. The native alternative gives you the same cascading purple flowers on a far more manageable plant:

• American wisteria (W. frutescens): NC State Extension lists it for zones 5–9. 'Amethyst Falls' is the most widely sold selection; The Morton Arboretum notes it starts flowering at 2 to 3 years old.
• Kentucky wisteria (sold as W. macrostachya): NC State Extension and the Lady Bird Johnson Wildflower Center treat it as part of the same native species, W. frutescens.

One caveat from UMD: American wisteria does not naturally occur in Maryland and may become weedy in natural areas there, so check your state's native plant guidance. UMD also suggests other native flowering vines such as trumpet honeysuckle (Lonicera sempervirens), crossvine (Bignonia capreolata) and virgin's-bower clematis (Clematis virginiana). Butterfly bush raises a similar question; see butterfly bush invasive status by state. For other regional natives, see native plants for the Northeast and native plants for the Southeast.

Wisteria vine or wisteria tree?

Wisteria is naturally a vine. A "wisteria tree" is a vine trained as a standard: a single trunk staked upright, with the top pruned into a head of branches. Any species can be trained this way, and "tree form" plants sold at garden centers are often Asian wisteria. If you want the tree look, buy or train American wisteria instead.

1. Choose one strong stem and train it straight up a sturdy stake (metal or rot-resistant post) as it grows; the RHS notes a vertically trained stem is usually stronger than a twined one; remove all other stems.
2. Rub off side shoots on the lower trunk as they appear.
3. When the stem reaches the height you want, pinch the tip to force branching, and let the top branch out.
4. Prune the head every summer and winter (below) to keep it compact. Keep the trunk staked for several years until it is thick enough to stand alone.

How to plant wisteria

1. Choose full sun. Per UMD Extension, wisteria grows best and flowers more abundantly in full sun; a shaded vine makes leaves instead of blooms.
2. Build or pick the support first. Even American wisteria becomes a woody vine that needs a strong pergola, arbor or heavy-gauge wire system. Asian wisteria grows large trunks that can crush light trellises and pry apart siding and gutters; do not let any wisteria climb a house or tree unsupervised.
3. Plant in spring or fall in moist, well-drained soil. Dig a hole as deep as the root ball and twice as wide.
4. Keep the graft above ground. If the plant is grafted (look for a knobby union near the base), set it so the union stays above the soil line.
5. Water deeply at planting and through the first summer during dry spells.
6. Skip the nitrogen. Wisteria is a legume and rarely needs feeding. High-nitrogen fertilizer, including lawn fertilizer that drifts into the bed, promotes leafy growth instead of flowers.
7. Train early. Tie the main stems to the support and choose the framework you want before the vine decides for you.

When wisteria blooms, and why it might not

Asian wisteria flowers earlier, opening on bare stems before the leaves emerge (UMD Extension). American wisteria blooms later, after leaf-out: NC State Extension gives April–May in North Carolina, the Lady Bird Johnson Wildflower Center gives May–June, and the Morton Arboretum lists summer flowering in the Chicago area. NC State notes limited additional summer bloom may occur. Exact timing shifts with your zone and the season.

How to prune wisteria

Wisteria needs regular pruning to flower well and stay in bounds. The RHS recommends pruning twice a year:

1. Summer (July to August): cut the long, whippy green shoots of the current year back to about five or six leaves from the main framework. This controls size and helps flower buds form.
2. Winter (January to February): cut those same shoots back further, to two or three buds. The short spurs that remain carry the next spring's flowers, and the fat flower buds are easy to tell from slim leaf buds in late winter.

For American wisteria, The Morton Arboretum gives a similar two-step routine: after flowering, prune excess growth back to 6 inches, and in winter cut again so each stem has two to three buds left. NC State Extension adds that any drastic pruning is best done in spring, immediately after flowering. On any wisteria, remove suckers and ground runners as soon as you see them. Timing for your other shrubs and vines is on the pruning calendar.

Removing Asian wisteria

Established Chinese or Japanese wisteria is persistent, and University of Maryland Extension warns that root fragments left in the ground can sprout. The North Carolina Forest Service fact sheet outlines the approach:

1. Pull or dig small infestations by hand while they are still small; extensive roots and runners make manual removal impractical on large patches.
2. For vines climbing into trees, cut each stem near the ground and again higher up, and remove the cut section. Treat the freshly cut stump with a triclopyr herbicide, following the label exactly. It is often impossible to pull every vine out of a canopy, but treated vines die rather than keep spreading.
3. For ground-covering wisteria, the fact sheet recommends a foliar spray of 2 percent glyphosate or triclopyr, wetting all the leaves, applied from spring through fall when air temperatures are above 65°F.
4. Expect repeat treatments, and check the site for several years for resprouts and seedlings.

For telling wisteria from other invasive vines and broader removal methods, see invasive vines in eastern North America.

Is wisteria poisonous?

Yes. The ASPCA lists wisteria as toxic to dogs, cats and horses, naming lectin and wisterin glycoside as the toxic principles. Clinical signs listed include vomiting (sometimes with blood), diarrhea and depression. NC State Extension lists the seeds as the poisonous part and notes that eating one or two seed pods can cause nausea, frequent vomiting, abdominal pain, depression and diarrhea. Pick up fallen pods where pets or children play, and call a veterinarian, pet poison line or Poison Control if anyone eats part of the plant.

Common mistakes

Frequently asked

Is wisteria invasive?

Chinese (Wisteria sinensis) and Japanese (W. floribunda) wisteria are invasive in many eastern and southern states, where they escape into woods and smother trees. American wisteria (W. frutescens) is native and is the recommended alternative.

Is American wisteria invasive?

No. American wisteria is native from Virginia to Illinois, south to Florida and Texas (NC State Extension), and is less aggressive than Chinese wisteria. University of Maryland Extension notes it does not naturally occur in Maryland and may become weedy in natural areas there. It still needs a sturdy support and regular pruning.

When does wisteria bloom?

Chinese and Japanese wisteria bloom earlier, on bare stems before the leaves emerge. American wisteria blooms later, after leaf-out: April–May in North Carolina per NC State Extension, later in colder areas, and it can rebloom lightly in summer.

Is wisteria a tree or a vine?

Wisteria is a woody vine. A wisteria tree is a vine trained on a single staked trunk and pruned into a rounded head, a form called a standard.

Is wisteria poisonous to dogs?

Yes. The ASPCA lists wisteria as toxic to dogs, cats and horses, with vomiting (sometimes with blood), diarrhea and depression as signs. Keep pets away from seed pods and call a veterinarian if one is eaten.

How fast does wisteria grow?

University of Maryland Extension describes Asian wisteria as rampant, able to climb over and kill mature trees. American wisteria is less aggressive but still large: the Morton Arboretum puts it at 20 to 30 feet long, and NC State Extension lists heights of 15 to 40 feet.

Can I grow wisteria in Florida?

Yes, choose American wisteria, whose native range extends south to Florida (NC State Extension) and which the Florida Museum suggests as a Florida-friendly alternative. Avoid Chinese and Japanese wisteria, which have escaped into natural areas there.

Can wisteria grow in a pot?

It is a large woody vine, so a pot is a short-term option at best. A compact, early-flowering selection of American wisteria such as 'Amethyst Falls' is the most practical choice, with a sturdy support and the same twice-yearly pruning. Asian wisteria is too vigorous for pot culture.

Sources

1. Chinese and Japanese Wisteria, University of Maryland Extension
2. Wisteria frutescens (American Wisteria), NC State Extension Plant Toolbox
3. American wisteria, The Morton Arboretum
4. Invasive Plant Fact Sheet 20: Japanese and Chinese Wisteria, North Carolina Forest Service
5. Asian Wisteria (invasive plant factsheet), Master Gardeners of Northern Virginia
6. Five facts about wisteria in Florida, Florida Museum of Natural History
7. Wisteria pruning guide, Royal Horticultural Society
8. Toxic and Non-toxic Plants: Wisteria, ASPCA Animal Poison Control
9. Wisteria frutescens (American wisteria), Lady Bird Johnson Wildflower Center

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