Bohemian knotweed (Polygonum x bohemicum) and three other knotweeds — Japanese, giant, and Himalayan — are members of the buckwheat family that aggressively spread through underground root systems and their wind-blown seeds.
Native to eastern Asia, knotweeds were introduced to North America in the late 1800s. They thrive in sunny moist areas by rivers and streams, roadsides, rights of way, and disturbed ground. Knotweed can grow up to 8 feet tall in clumps, with reddish stems that are smooth, hollow and jointed. Some people mistake it for bamboo.
The matted root system can spread underground for more than 30 feet, and pieces of root and stem as small as 1 inch can sprout after being moved by floods, machinery or people. Knotweeds’ quick, determined growth crowds out native plants.
Digging knotweed isn’t recommended because it’s difficult to obliterate all of the rootstalk. For details about mechanical and chemical ways to curb its growth, contact the Whatcom County Noxious Weed Control Board.