Fallopia japonica, commonly known as Japanese Knotweed, is an invasive species resembling bamboo. Originally used as an ornamental garden plant on estates, Japanese Knotweed established itself by the mid 1890’s as a rapid-spread invasive plant quickly moves outward from gardens and becomes unmanageable. Japanese Knotweed has spread to 42 states from coast to coast, and eight Canadian Provinces.
A member of the buckwheat family, Japanese Knotweed grows up to 15 feet tall with leaves that grow 6 inches long and 4 inches wide. From August to September sprays of small greenish-white flowers bloom from the stalks. Large root networks called rhizomesgrow 65 feet or more horizontally and ten feet deep into the soil, making it difficult to eradicate. If severed, a section of root or stem may sprout and form a new plant, often foiling removal attempts. Able to withstand deep shade, high temperatures, high soil salinity, and drought, Japanese Knotweed spreads rapidly and forms dense thickets that crowd out and shade native species. This plant is extremely persistent and hard to exterminate once it has been established.
The United Kingdom has suffered from the weed so severely that banks will decline a mortgage request if Japanese Knotweed is found growing on or around a property. The country has listed the invasive as one of the only two terrestrial weeds restricted under the Wildlife and Countryside Act of 1981, making it illegal to plant. The cost of control in the United Kingdom is thought to be in the tens of millions in US dollars per year. Costs in the United States are comparable. The economic damage comes in the form of pesticides, revegetation, and reconstruction of affected properties such as parking lots.
According to the New York State Department of Conservation (DEC), Japanese Knotweed is listed under prohibited invasive species. Following the terms of their regulations, “no person shall sell, import, purchase, transport, introduce or propagate any prohibited invasive species.”
Find native alternatives for your garden at PlantDontPlant.org!