Knotweed grows naturally along rivers and banks. A native of Asia, knotweed's aggressive habits tend to choke out other plants and take over large areas of soil. Two common varieties, Japanese knotweed and giant knotweed, thrive in many areas of the United States, China, Japan, Great Britain and Canada. Although these plants pose problems for farmers and gardeners, they do provide some beneficial purposes.
According to the U.S. Environmental Protection Agency, this plant can help protect other types of vegetation from pest infestations. An extract from the giant knotweed is an active ingredient in a biopesticide. Used as a non-food crop application in greenhouses, this ingredient helps to control cases of powdery mildew. This spray may help boost the plants' natural defense mechanisms, encouraging healthy growth in ornamental varieties of plants.
Knotweed grows where other plants can't survive, enabling it to provide a cover of green in barren areas. Ground covers help cool the soil and hold in moisture. However, without proper control measures, this aggressive plant may spread into desirable areas of the landscape, posing a hazard to nearby plants.
As part of traditional Chinese medicine, the extraction of certain compounds from knotweed plants may treat some medical conditions, notes Andrew Bartlow and colleagues from Wilkes University. An organic compound known as resveratrol may help thin the blood, reducing inflammation and edema. This drug shows some promise in treating certain types of cancers, including breast cancer. Other compounds in knotweed may help treat cardiovascular disease.
Grown in areas that experience occasional flooding, knotweed can protect against soil erosion. Their long roots and rhizomes help hold the soil in place when rising or rushing water threaten to wash away the soil.