Invasive Knotweed in Snohomish County

Legal Status

The four species of knotweed, Japanese knotweed (P.cuspidatum), giant knotweed (P.sachalinense), Bohemian knotweed (Polyganum x bohemium) and Himalayan knotweed (Persicaria wallichii) are present throughout Snohomish County. Although knotweed is a Class B noxious weed, the county will not enforce if knotweed is present on private or public land. Instead, voluntary control is encouraged to prevent knotweed from spreading to neighboring properties.

What does Knotweed look like?

Knotweed grows in dense stands, six to twelve feet tall. Its leaves are heart shaped, lance-shaped, or triangular. It has spikes of small, white flowers in later summer. It has bamboo-like, hollow stems.


How does Knotweed spread?

Even the smallest fragment of a knotweed plant will sprout roots and grow. That’s why it’s important to properly dispose of knotweed. Do not dump plants in vacant lots or leave cut stems in or along rivers where they could be moved and invade new areas.