Invasive Knotweed

What is Knotweed and what is the City doing about it?

Knotweed refers to several species of tall, perennial, invasive plants from Asia that have overrun numerous streamside and roadside areas in western Washington. Knotweed can be identified by its long, hollow, bamboo-like stalks, and large smooth-margined leaves. Sprays of white flowers are visible in late summer. Knotweed spreads aggressively, and it can severely degrade wildlife habitat, push out native plants, and increase erosion. If it is mowed, dug up, or cut, stray fragments will start new plants. Because it grows rapidly to between 6 and 15 feet tall, it can dangerously reduce visibility on roads. Its spreading rhizomes can even grow up through asphalt, damaging driveways and parking areas! In recent years, the City has tracked and controlled knotweed in a number of locations on the Island - please let us know if you see it by contacting us at restoration@mercerisland.gov

Learn more about knotweed at this King County page.