Invasive Plant

Giant knotweed

Reynoutria sachalinensis

Warning

All knotweeds species in BC can grow through concrete and asphalt, damaging infrastructure. This can result in significant control, management, and repair costs.

About This Species

Knotweeds were introduced to British Columbia for use in gardens and landscaping due to their rapid growth and attractive appearance. Giant knotweed is native to Asia and Russia. There are now four species established in BC: Bohemian (Reynoutria x bohemica), Giant (Reynoutria sachalinensis), Himalayan (Persicaria wallichii), and Japanese knotweed (Reynoutria japonica). Knotweeds grow aggressively and are very hard to kill. Giant knotweed is the largest of the species, with leaves about twice the size as those found on the other species. They are widespread throughout the province, and are often found in riparian areas, derelict land, road and railway right of ways and gardens. They thrive in moist soil and full or partial sun. Knotweeds can spread by seed, root fragments, and stem fragments, making them very difficult to control. Giant knotweed is designated as a Provincial Noxious Weed by the BC Weed Control Act, as well as a Regional Containment/Control species by the BC Provincial Priority Invasive Species List.

How to Identify

Giant knotweed has bamboo-like hollow green stems, sometimes with reddish-brown speckles up to 5 m in height. Stems may persist through the winter as bare, grey- or straw-coloured hollow stalks.

Giant knotweeds have attractive plumes of small, white to green flowers in the spring.

Leaves are predominantly heart- to triangular-shaped, 16-20 cm wide, 30 cm in length.