Japanese knotweed is a smooth, reddish-brown, jointed stems that grow three to ten feet tall. Its leaves are six inches long by four inches wide, oval or triangular, and pointed at the tip. Their flowers are small, white or green, and grow in drooping clusters.
This species originated from Asia as an ornamental. Japanese knotweeds are aggressive and forms thickets that completely exclude indigenous turfs. As frost kills the plant above ground, it can spread from deep underground. It can be spread by seed and can tolerate partial shading. It can survive severe floods. Chemicals in the roots of the weed exclude other plants nearby. Small pieces of the plant can root and grow. Washington State concludes this weed as Class B which means it should be within current boundaries to prevent further spread.
This species originated from Asia as an ornamental. Japanese knotweeds are aggressive and forms thickets that completely exclude indigenous turfs. As frost kills the plant above ground, it can spread from deep underground. It can be spread by seed and can tolerate partial shading. It can survive severe floods. Chemicals in the roots of the weed exclude other plants nearby. Small pieces of the plant can root and grow. Washington State concludes this weed as Class B which means it should be within current boundaries to prevent further spread.