Dense stands of Japanese knotweed exclude native and other desirable vegetation and reduce wildlife habit. It decreases water flow through rivers and streams and thereby contributes to flooding. It is a long-term threat because it occupies edges of woods and waterways that are valued for biological and visual diversity. It is one of the most troublesome weeds along railway rights-of-way, and is said to create a fire hazard in the dormant season.
Japanese knotweed is highly regarded for its attractive flowers and has been planted by beekeepers for its nectar. It is also prized for its tolerance of harsh conditions like rocky soils with limited nitrogen and low pH. It has been planted along highways to control soil erosion and has been used for revegetation of strip-mine spoil and to stabilize land affected by volcanoes.
Japanese knotweed has caused damage to sidewalks and parking lots where shoots have been able to grow up through concrete.
Fast-growing branch tips picked in spring are said to be have a unique almond-like flavor when prepared in the manner of rhubarb pie.
Japanese knotweed was used in folk medicine as a laxative, but contains tannins that are carcinogenic and inhibitors of digestive enzymes.
The dense, hedge-like growth of Japanese knotweed was commonly used as a screen around out-houses.
