One of the great things about spring at Hilton Pond Center and most places in temperate North America is the sudden appearance of colorful blossoms after a relatively drab winter. This year's flower set--perhaps because of plentiful rain over the past several months--seems especially full, with a succession of Eastern Redbuds, Chickasaw Plums, and Flowering Dogwoods to brighten the landscape. One plant that seems to have an unusually heavy flower set this year smells good, looks even better, but acts very, very bad.

For the past few weeks, Piedmont treetops (including a few at Hilton Pond) have been festooned with an attractive blanket of pale white and purple--the unmistakable blossoms of Chinese Wisteria. This hardy vine--imported from Asia because of its rapid growth, eye-pleasing flowers, and dense foliage--may start out being the landscaper's friend, but fairly quickly it demonstrates why we should be ever so careful about flora we import and plant in our yards. Yes, it seems that Chinese Wisteria is one non-native beast that truly fits the category of "Invasive Plants."

Folks in the Southeastern U.S. are familiar with Kudzu, another Asian import that runs rampant over trees, telephone poles, old buildings, and slow-moving children. As bad as Kudzu is, Chinese Wisteria is even worse; Kudzu simply climbs and covers native trees and shrubs--occasionally shading them out and killing them---while Chinese Wisteria almost always strangles them to death. Wisteria is a twining vine, and when it wraps around a tree trunk the combined growth of vine and tree eventually chokes off the tree's plumbing. After the host tree rots away or topples earthward, the wisteria simply grows along the ground until the delicate tip of a new stem finds another vertical object to ascend, and the murderous cycle repeats itself.

As its blossom reveals (top and above right), Chinese Wisteria, Wisteria sinensis, is in the five-petalled Pea Family (Fabaceae); members of the subfamily that contains wisterias have flowers in which one petal forms a hood over four others; two of these form "wings," and two others are fused to form a pouch or keel. In wisterias--named for American anatomy professor Caspar Wistar--there are multiple one-inch flowers that form a pendulous raceme (cluster) at the end of new growth. In spring, the flower cluster emerges first, followed soon after by a spray of pinnately compound leaves with 9-11 leaflets. These start out purplish- red but turn dark yellow-green at maturity. As legumes, wisterias apparently do host nitrogen-fixing bacteria that enrich the soil--NOT an attribute that offsets their tree-killing tendencies. (Oh, and by the way, wisteria seeds cause mild to severe gastic distress when ingested by humans, and as few as 2-3 may be toxic to children.)

Chinese Wisteria has been planted in North America as an ornamental since first imported in 1816, and it almost seems plausible that some of those original lianas could still be around. A mature Chinese Wisteria--whose vine is as hard and woody as many trees--can be 65 feet tall and 15" or more in diameter. (Such large growth usually occurs on cliffs or human-made structures, since a wisteria of this size likely would have killed its supportive plant host years ago.) Wisteria often branches at or near the surface of the ground, sending out runners in all directions and propagating vegetatively, but the prolific blooms also produce copious pollen--visible on the flower in the top photo--that fertilizes a neighboring blossom and results in distinctive velvety green pods containing shiny brown seeds (below). These seeds can be carried far downstream until entire watersheds are sometimes lined by native trees infested with Chinese Wisteria.

One problem with the importation of Chinese Wisteria is that horticulturists selected varieties that were robust and tolerant of a wide variety of soil and water regimes. In addition, they were careful NOT to bring along any of wisteria's natural diseases or insect pests. This strategy had a good aspect: At least they didn't introduce bugs that could have jumped to native North American flora; the downside is that there was nothing on this continent to keep wisteria populations in check. To make matters worse, Chinese Wisteria is not controlled initially by mechanical cutting--the remaining rootstock simply rears back and sends out ten times more shoots than before. Some native plant enthusiasts have had good luck with whacking back the same Chinese Wisteria every month for several years in a row, a strategy that eventually exhausts whatever reserves are stored in its roots. This is what we've been trying at Hilton Pond Center for the past 21 years, and we're finally starting to see some progress! Unfortunately, a former owner of the property seems to have planted sprigs of Chinese Wisteria in numerous spots around the property and it's about all we can do to locate and annihilate shoots as they emerge. Thus, each spring--despite our efforts--we always glance out through the woods and see a new cluster of blue Chinese Wisteria blossoms near the top of some tree that we somehow missed.

One effective method of control is to immediately treat a newly cut stem with strong herbicide; this would likely help us in our quest to eliminate Chinese Wisteria, but it's a technique we'd rather not use at the Center if we can avoid it. What we might do instead is purchase a bunch of American Wisteria, W. frutescens. This native wisteria is less aggressive than the foreign invader, and perhaps we could to teach it to wrestle with W. sinensis enough to slow down growth of the latter. American Wisteria (above), found in the Carolinas mainly along the Coastal Plain, has individual flowers similar to those of its Asian counterpart, but they often form racemes that are more compact; in addition, the American plant's individual leaflets are broader and usually more numerous (9-15). American Wisteria also tends to flower much later in the year than early-blooming Chinese Wisteria. A third species with white bark--W. floribunda, or Japanese Wisteria--is much less common in the Carolinas and very similar in appearance to W. sinensis. The best way to tell them apart is almost like a bad joke: Japanese Wisteria twines around its host in a clockwise manner as seen from above, while Chinese Wisteria goes the opposite direction.

We'd really rather not have any Oriental wisterias at Hilton Pond Center. These invasive plants damage native trees and shrubs, and they're a pain in the neck to cut back as they try to cross our walking trails to get to an unsuspecting tree on the other side. We could train them on an arbor as is done at botanical gardens (above left), but the best way we've heard to control wisterias is to put them in little tiny pots and turn them into bonsai (right). That way, Chinese Wisteria and Japanese Wisteria can still smell and look good, but they will never get big enough to be really, really bad.

SPECIES BANDED THIS WEEK
Ruby-throated Hummingbird--1
Chipping Sparrow--3
Dark-eyed Junco--1
Ruby-crowned Kinglet--1*
Song Sparrow--1
Northern Cardinal--2
Eastern Towhee--2
Gray Catbird--1*
White-throated Sparrow--9
American Robin--1*

* = New species for 2003

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