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Giant knotweed
Photo Credit: Leslie Mehrhoff, University of Connecticut, Retrieved from (Image Number: 5447655), used under CC BY 3.0 US, modified from the original

Common Name: Giant Knotweed

Scientific Name: Fallopia sachalinensis

Habitat: disturbed areas, grassland wet, forests - wet areas, forests - open areas, forest edges, ditches

Provincial Designation: Prohibited Noxious

Prohibited Noxious weeds are plant species designated in the Alberta Weed Control Act. Prohibited noxious weeds must be destroyed when found, meaning all growing parts need to be killed or the plant's reproductive mechanisms need to be rendered non-viable.


Giant knotweed is native to northern Japan. It was introduced into North America as an ornamental due to its size and white flower clusters.

Legislated Because

This species forms dense stands that shade and crowd out native vegetation causing a loss or alteration of wildlife habitat, especially along waterways. It can also sprout through asphalt and small cracks in concrete causing structural damage to foundations and roads.


Giant knotweed has small white flowers that are 3-5 mm wide and are clustered together in showy often upright sprays along the branches.

The large leaves are heart-shaped and grow up to 45 cm long and 30 cm wide. The undersides of leaves are covered in soft, 0.2-0.6 mm long hairs.

The stems are round and hollow and grow up to 4 m tall. There are solid nodes in the stem. The fast-growing, bamboo-like stems can grow 4-5 cm per day.

Learn more about this species:

See Fact Sheet - Alberta Invasive Species Council

For More Information

Weed Identification


In Edmonton: 311

Outside Edmonton: 780-442-5311


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