Japanese knotweed is one of many invasive plants that have established itself in North America. Most people have had to deal with Japanese knotweed at one time or another, but does everyone know what the plant is or its full impact on the environment? This article will provide pointers on recognizing Japanese knotweed, in order to combat it.
Japanese knotweed is an herbaceous perennial. This means the plant dies to the ground in winter, but emerges anew in spring. Since the dead stems persist well into the next growing season, the plants can be seen during all seasons. Japanese knotweed grows in dense clumps, reaching six to ten feet in height often. Resembling bamboo, the hollow stems have joints every six to eight inches. Leaves, and later, branching stems emerge from these junctions.
In spring, the new shoots emerge from the clumps, quickly growing to a few feet before the developing leaves spread out. They are predominately green but with red speckles or sometimes all red at the joints. The stems can get over an inch thick. They grow straight out from the ground before branching, and as the season’s growth matures, the main stems will arch outward from the clump, forming a bush that is often as wide as it is tall.
The leaves of Japanese knotweed are heart shaped to round, roughly four to six inches wide and slightly longer. They are alternate; drooping downward as the branches arch. White clusters of flowers are borne from the leaf axils, the bloom time is in late summer. The seeds quickly mature and are dispersed, usually by wind.
Once the frost hits, the plants die down to the ground. The dead brown stems and seed structures that remain persist well into the winter, and thus the plant can be recognized during every season.
Valued long ago for its beauty in all seasons along with its ability to control erosion, Japanese knotweed has proven to be an aggressive invasive, crowding out native plants and adversely affecting wildlife. Therefore, the recognizing and controlling of this plant is a matter of great importance.