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Knotweed: What it Is and What to Do

Knotweeds can grow between 10 and 20 cm a day and can reach a height of between 1.5 m to 6 m. Knotweed spreads primarily by underground rhizomes.

There are four different types of knotweed in our province, three of which have been found in the Boundary.

In 2015, the Boundary Invasive Species Society (BISS) found giant knotweed (Fallopia sachalinensis) while surveying Kettle River.

There are a number of sites of Japanese knotweed (Fallopia japonica) in the Boundary area, but most of it is bohemian knotweed (Fallopia bohemica). Bohemian knotweed is a hybrid of Japanese and giant knotweed. A lot of it is being grown in people’s yards and it is starting to escape.

The Ministry of Agriculture & Lands designates Knotweed as Provincial Noxious, which means it must be controlled. Knotweed can grow through asphalt and concrete. It can grow through foundation walls, come up through floorboards, and up through walls of the house.

Knotweed is native to Eastern Asia and is also sometimes called ‘false bamboo’. The stems are hollow with reddish-brown speckles, leaves are bright green and are heart, or triangle-shaped. It also has creamy white flowers that grow in drooping clusters. 

Knotweeds can grow between 10 and 20 cm a day and can reach a height of between 1.5 m to 6 m. Knotweed spreads primarily by underground rhizomes. The roots can spread 20 m laterally and 3 m deep.

Knotweed can grow from root fragments which can remain dormant in the soil for years. Their extensive root systems make it difficult to control because it can sprout even after many years of control. Cutting down knotweed is not effective as it stimulates the roots to spread farther when it gets cut. It is possible to dig knotweed out, but that would require a machine and the material would need to be buried extremely deep to keep it from growing.

The most effective method of treatment is herbicide, where a hired spray contractor will treat the knotweed. Please do not share this plant to friends or family.

Native alternatives include oceanspray, saskatoon berry, and black elderberry.

For more information, please contract the Boundary Invasive Species Society at 250-446-2232, on Facebook, info@boundaryinvasives.com or check out our website www.boundaryinvasives.com.

Jen Haynes is the Education Coordinator for the Boundary Invasive Species Society and can be reached at www.boundaryinvasives.com or 250-446-2232