As often happens, this monster was imported from Asia in the late 1800s as ornamental shrubbery. It would probably make a great privacy fence. That being said, you really don’t want this stuff in your yard.
It has spread from Maine to Minnesota and as far south as Louisiana. The Minnesota Department of Agriculture says it is now in 41 states. It has been found in St. Louis and Lake county in northeastern Minnesota, and Ramsey , Washington and Sherburne in the east central area. Duluth has found it growing, not only in back yards, but in their wooded parks. The city’s invasive species inspector, Judy Gibbs says “it is just exploding up and down the banks along Keene creek.”
So what make this such a problem? For one thing, it is extremely difficult to kill. It tolerates full shade, high temperatures, high salinity, drought and flooding. It recovers from flooding before the native plants do causing the D.N.R. to label it a “significant threat.”
Eboney Jewelwing, a damselfly in danger due to the Japanese knotweed.
Killing this stuff is tough. Fire doesn’t help. If you cut off one stem, another grows faster from the roots. Pulling out the roots can work but it is very difficult and impractical for large areas. The same hardiness that made the plant so useful in our severe planting conditions is the same thing that makes it so hard to kill. Judy Gibbs says “this stuff grows so fast, people say you can see it grow.” It not only displaces the native plants, but the insects that need those plants. Streamside habitats are the only place you will find a little damselfly called the eboney jewelwing. “It would be a shame if we lose that little guy because of bamboo,” she says.
So far, the only thing that kills Japanese knotweed is chemicals.
Unfortunately, knotweed is just the latest in a long line of aquatic and terrestrial invaders introduced from other countries. Plants, trees and shrubs from Asia seem to do exceptionally well here. Other introductions are garlic mustard, quack grass, introduced as pasture grass, dandelions, earth worms, spotted knapweed, purple loostrife, and buckthorn to name a few. Since the invaders aren’t susceptible to our native diseases, they tend to thrive. Think about this if you are ever tempted to sneak a plant into the country from one of your overseas travels. It may be beautiful where it is, but plants are kept in check by, not only climate, but soil type, predators and diseases that probably don’t exist here. Enjoy, but what you see there, leave there. Bev. Johnson M.G.