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Giant Knotweed (Polygonum sachalinense)       



Giant knotweed


Stems of Giant knotweed are usually thicker and less mottled than Japanese/ Bohemian knotweed.
Stems of Giant knotweed are usually thicker and less mottled than Japanese/ Bohemian knotweed.

Giant knotweed is a perennial that blooms July to October. It grows over 12 feet tall and is closely related and similar to Japanese Knotweed. The leaves are heart shaped and often exceed one foot long. The creamy white flowers are sparse and the flower size does not increase with maturity. Giant knotweed hybrids with Japanese knotweed (Bohemian knotweed) are common. Japanese knotweed is smaller with truncate leaves.

Giant knotweed is the largest of the knotweeds, enabling this species to dominate and out compete native or beneficial plants. It poses a significant threat to riparian areas where it prevents streamside tree regeneration. Research indicates that giant knotweed produces allelochemicals from the roots, which aid in its dominance and rapid colonization. Giant knotweed is a viable pollen source for Japanese knotweed, resulting in male fertile hybrids which are often confused with Japanese knotweed. (From Oregon Dept. of Agriculture)

Brad Bluemer, Bonner County Weed Superintendent, stands in front of Giant knotweed which can grow over 12 feet tall.
Brad Bluemer, Bonner County Weed Superintendent, stands in front of Giant knotweed which can grow over 12 feet tall.

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