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The Monday Garden
Invaders: Asiatic Bittersweet

Issue No. 126 - August 22, 2004
by Sue Sweeney

When I was a child in upstate New York, we treasured the American Bittersweet, Celastrus scandens, a rare and beautiful plant on the local endangered list. Today, on the Connecticut shoreline, I pull up a lot of its Asian cousin, the Oriental or Asiatic Bittersweet, Celastrus orbiculatus.
 

picture: Asiatic Bittersweet (Celastrus orbiculatus) through out the year in downtown Stamford, CT

 
The native plant grows 10’ to 20’ vines and spreads slowly. Its natural range is Ontario to Manitoba, south to North Carolina and New Mexico (Zones 3- 8). It has separate male and female plants and is bee-pollinated. Its berries are munched up by chickadees, blue jays and mockingbirds, to name a few. It is late-winter survival food for many species, including squirrels. (“Late-winter survival food” means that they don’t like it a whole lot but will eat it when they have to.) The berries aren’t fatal to humans but shouldn’t be eaten because they are guaranteed to clean out the alimentary system in short, albeit painful, order.

The beautiful but deadly invasive cousin, a native of Eastern Asia, Korea, China, and Japan, was first imported to North America in the 1860’s.

Ironically, it was a favorite of conservationists as a quick growing groundcover that provided shelter and food for wildlife, protected against soil and dune erosion, had a 95% seed germination rate, made great material for floral arrangements, and had attractive golden-yellow fall foliage.

How could you lose? Well, if you wanted an awful lot of the stuff, growing 60’ vines, to the exclusion of a more diverse community, you couldn’t. It’s now in 33 states from Connecticut to North Carolina and west to Illinois. Because its as salt tolerant as its American cousin, it’s particularly a problem around the Long Island Sound. It’s now reaching up in Ontario. However, those of you out West can still beat it back.
 

Picture: Asiatic Bittersweet (Celastrus orbiculatus) in flower Spring 2004 Hoyt Street Ally, Stamford CT

 
You often spot the invader in the form of seedlings under any tree where birds roost. In the mulch under a street elm in Downtown Stamford the other day, the weed population was 15 bittersweet seedlings, one woodbine, and 2 crab grass. This should give you an idea of the plant’s ability to spread.

The adult Asiatic Bittersweet’s leaves are rounded with pointed tips and finely-toothed margins. The leaves can be almost lime-green in spring, maturing the mid-green and then yellowing as the berries ripen in August. Finally, just past the high of the fall color, the leaves will be a spectacular golden-yellow for a week or two.

Asiatic Bittersweet has small green-white flowers in late spring. The female plants then follow through with clusters of round green berries that grow to pea size. The berries turn yellow, then orange. In the early fall, they split to reveal the bright red inner fruit. The fruit persists until munched up by the fauna in January or February (or until you throw out the wreath that the florist made from it).

Asiatic Bittersweet makes a twining, woody vine that kills supporting plants by strangling and shading. Many host plants also succumb to wind and ice with the added weight of the vine. The invader uses root suckering to spread until it’s a dense thicket. The vine can swell over time into a 4” diameter trunk with exfoliating bark.

Asiatic Bittersweet spreads rapidly between locations by prolific, bird-carried seeds. Every winter, at the local supermarket, the sidewalk beneath the English sparrows roost is red with Asiatic Bittersweet rinds which have passed through the birds’ stomachs.

 

Picture: Asiatic Bittersweet (Celastrus orbiculatus) flower buds Spring 2004 Hoyt Street Ally, Stamford CT

 
The drive to control the Asiatic bittersweet has further endangered the American native because the two plants look so similar. To make matters worse, there are reports of interbreeding.

Differences between the native and its invading cousin.

• The Asiatic flowers and fruits at the branch tips and in the joints between the leaves and the stem; the American flowers and fruits only at the branch tips.

• The Asiatic can grow to 60; the American usually only makes 10’ to 20’.

• The Asiatic has yellow to yellow-orange seed covers; the American has orange seed covers.

• The Asiatic has bright red seeds; the American’s seed are less bright, sometimes more orange.

• The Asiatic grows very quickly: the American’s a slow grower.

If a small bittersweet seedling or vine appears in your garden, along your roadside or in your woodlot, you can be pretty sure it’s Asiatic. I don’t recommend waiting until it grows up and fruits (and becomes impossible to root out) to make sure it’s not one of the good guys.

Controlling the Asiatic Bittersweet:

• you can manually remove by pulling up all (yes, every little bit) of the root; this works well with seedlings and small plants.

• larger plants can be repeatedly cut to the ground (at least 3 times a season)

• After cutting to the ground, particularly in late summer- early fall, when the plant is sending its stores down into the roots for winter, the stumps can be (carefully) painted with an appropriate herbicide. Always use 'cides sparingly, as a last resort, with great caution, and according to the label.

• Seed bank lasts several years and birds will frequently re-seed near roosting areas, so continue monitor the area at least twice a season for seedlings.

Lastly, kill the berries from wreaths and uproots plants by baking them in the sun for weeks in a sealed black plastic bag. If you dump the uprooted plant or a wreath in the garbage, guess what you get at the dump? More bittersweet! Indeed, discarded floral wreaths have been a major cause of seed dispersal.

 

Pictures: samples of Asiatic Bittersweet (Celastrus orbiculatus) leaves

 

picture: Asiatic Bittersweet (Celastrus orbiculatus) vine strangling a choke cherry tree, Hoyt Street, Stamford CT 2004

 

picture: detail of the above Asiatic Bittersweet (Celastrus orbiculatus) vine’s trunk.

 
Further Reading:
From The Monday Garden. Copyright © by Sue Sweeney. Reproduced with permission. 

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