Japanese Knotweed, considered the scourge of gardens, is a highly invasive perennial shrub that is now classified as a noxious weed. It grows up to 10 feet tall and spreads rapidly by underground rhizomes and by seed with a root system that can be up to 10 feet deep and over 20 feet wide, displacing other plant life and reducing wildlife habitats. How did it come to be in the U.S. and what can be done to stop it?
It arrived in the U.S. after first being imported to England. In 1850, German botanist Philipp von Siebold mailed a box of plant specimens to Royal Botanical Gardens, Kew. He could not have known what horrors he would be unleashing upon the world! Partly because of its properties of flowering very late in the season, it was widely promoted by people such as William Robinson, the author of The Wild Garden (1870) and The English Flower Garden (1883) as well as by nurseries.
By the late 1800s it had made its way to the United States. It is not known who first imported it. Though there is a rumor that it was Frederick Law Olmsted, there is no evidence to substantiate it.
In the U.K., the kind of regulations that govern the handling of toxic waste also apply to Japanese knotweed! The Environmental Act of 1990 requires that both the party removing the plants and the site receiving it must be licensed for handling Japanese knotweed. Planting or dumping knotweed in the wild is forbidden, punishable by a fine or imprisonment. In the U.S., 18 states, including Massachusetts, have laws governing knotweed, and an additional 10 have it listed on their invasive no-no list.
Many plant experts advise the best way to remove knotweed is to excavate in order to completely remove the roots. Apply glyphosate, cover the ground with plastic sheeting and leave it for at least a year. Retreating the area may be required over several years in order to completely eradicate it.
If you’ve given up the fight, you can always use the young shoots to make tea, beer, jam, pickles or a number of other culinary delights. Its taste has been compared to a very sour rhubarb. Take caution as it can only be used as a food source when the plant is very young!
Music:
String Quartet in D Minor, Op.56 by Jean Sibelius, performed by Orion String Quartet at the Isabella Stewart Gardner Museum
Photos:
Japanese Knotweed photos by U.S. Fish and Wildlife Service Northeast Region, Connecticut Gardener. Cambridge Brewing Company patio by David Drucker, Olmsted’s Folly by Cambridge Brewing Company