Fred Morgan J Hallworth ISC Dave Ingram D Tisseur

Plant Bio

Common Name:Japanese, giant, Bohemian and Himalayan Knotweed
Genus:Fallopia or Polystachyum
Species:F. japonica, F. sachalinensis, F. x bohemica, and P. polystachyum
Classification/Rank:Extremely Invasive
Method of Transportation:Root and stem fragments become dispersed through human activities or transported downstream by water.
Habitat/Range:Commonly found in gardens, from which it easily escapes. Newly disturbed soils with high moisture content. Also thrives in riparian zones and along stream banks and coastal areas.


Knotweeds (Fallopia and Polygonum spp.) are perennial garden escapees with hollow bamboo-like stems and wide leaves that are pointed at the tip. Flowers are found in the leaf axils and are greenish-white. Plants can grow to 3 m tall and can form very dense thickets. Knotweeds prefer moist to wet sites.

Japanese knotweed (F. japonica) has heart- to triangular-shaped on leaves that are 8 to 10 cm wide and up to 15 cm in length.

Giant knotweed (F. sachalinensis) is very similar to Japanese knotweed, but is much larger. It can grow to 6 m tall and its leaves are 20 to 40 cm long.

Bohemian knotweed (F. x bohemica) is the hybrid of Giant and Japanese knotweeds with characteristics from both plants.

Himalayan knotweed (P. polystachyum) is also similar in appearance, but its leaves are narrower than the other knotweed species.

Knotweeds are an extremely agressive invasive, even a small fragment of the root system can grow to form new plants, and it is strong enough to grow through the foundation of buildings!

The following three short animated videos provide good information: 1) Knot on My Property; 2) Identification, Reproduction and Spread of Japanese Knotweed; 3) What Knot to Do with Japanese Knotweed; as does the article "Are You Harbouring an Aggressive Alien Invader in Your Garden?".

If you have seen this plant or believe you may have it growing on your property please call the Weeds Hotline at 1-866-44WEEDS or report the site using the Report-A-Weed application.


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