Gardeners must check often for Japanese Knotweed shoots and treat them immediately. The Knotweed should be isolated before treating it, while being careful not to disturb the plant. The Japenese Knotweed should not be cut or removed because doing so may cause the plant to spread. The Knotweed should not be burned unless it is dried out.
Japanese Knotweed is a perennial with tall annual stems. The stems regrow each year from underground stems. In the spring and summer, shoots grow up to 7 feet tall and the leaves grow up to 5 1/2 inches in length. White flowers are produced in late summer and early autumn. Japanese Knotweed stems die during the winter. It does not produce seeds, but it grows back from small rhizomes.
The plant is native to Eastern Asia and was brought to England in the mid 1800s. In the late 1800s, it was brought to the United States and planted in gardens for pleasure and to control erosion. It began taking over vegetation and was deemed a problem in the early 1900s.
Japanese Knotweed is illegal to grow because of the damage it causes. The plant creates tall, thick thickets that block out sunshine for native plants. It can damage habitats for fish and wildlife and damage pavement. Japanese Knotweed is found in sunny areas around roads and riverbanks.