Japanese Knotweed was originally introduced from Asia as an ornamental and is still sometimes used in gardens. This highly invasive plant is found along roadsides and wetland areas where it out-competes native vegetation and is extremely difficult to control once established. It is known in BC along roadsides and moist climates especially in the south-west coastal region, but also in the Shuswap region and the Queen Charlotte Islands.

Biology 

Japanese knotweed is a herbaceous, semi-woody perennial member of the Buckwheat Family. It can grow 3 metres in height. Stems are stout, reddish-brown, round and hollow forming dense clumps resembling bamboo, giving rise to its other common names of Japanese and Mexican bamboo. Leathery leaves are egg-shaped, alternate and form at swollen joints along the stem. They are 10 to 15 cm long, flattened, rounded at the base with a pointed tip and are dark green above and lighter green below. Plant clumps produce rhizomes, which can extend 13 - 18 metres in length. Greenish-white flowers bloom in clusters along the stem, at leaf axils, from August to September.

Reproduction 

Primarily reproduction is vegetative through long creeping rhizomes or by root fragments, which readily produce new plants. Japanese knotweed root pieces are known to contaminate new sites through movement of dirt. When growing near water, root fragments can be carried down stream to establish new colonies. Escapees from deserted gardens are not uncommon.

Habitat 

Japanese Knotweed prefers open habitats and does poorly in the under-story of forested areas. It grows in a variety of soil types along roadsides, edges of waterways, neglected gardens and unused areas. It is known to grow in climates experiencing high temperatures and drought. Wetlands and moist, low-lying areas are the most common habitats.

Concern 

Dense stands, capable of crowding out all other vegetation, degrade native plant communities. It spreads quickly, is extremely aggressive and persistent and able to survive severe flooding. It poses a significant threat to areas adjacent to rivers, streams and other shore-lines where it can cause bank erosion. Clog waterways and lower the quality of habitat for wildlife and fish. During its dormant growth stages Japanese knotweed dries and can create a fire hazard.

“Bamboo-like” stems