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Japanese Knotweed - Overview

(Information below extracted from: 1. "A Review of the Biology and Ecology of Three Invasive Perennials in New York State: Japanese Knotweed, Mugwort and Pale Swallow-wort" by Leslie A. Weston, Jacob N. Barney and Antonio DiTommaso and 2. The Nature Conservancy Element Stewardship Abstract for Japanese Knotweed)

Japanese Knotweed is a member of the Polygonaceae family, originating from Asia. It was introduced to the United Kingdom in 1825 as an ornamental. It was introduced into the United States as an estate planting in the 1870's. By 1905, the invasive nature of Japanese Knotweed was already known and the Journal of the Royal Horticulture Society no longer advised its planting. The present range of Japanese Knotweed along the East Coast of North America extends from Nova Scotia to North Carolina. It is also well established in Washington, Oregon, Pennsylvania and Ohio.

Japanese Knotweed has bamboo-like stems that can grow as tall as 15 feet. It thrives in disturbed areas; however, once it is established in an area, it spread rapidly creating monoculture stands. It is a threat to natural areas; however, it does not appear to be a threat in low-light habitats.

The main means of spreading is via rhizome or stem fragments; even very small fragments can give rise to a new plant. In riparian areas, fragments are easily transported down-stream during storm events. Fragments can also be dispersed by human activity such as moving soil containing rhizome fragments.

The presence of large stands of Japanese Knotweed changes the habitat, shading out native vegetation, reducing species diversity and impacting wildlife habitat. The stands are extremely persistent and difficult to eradicate.

For much more information about Japanese Knotweed including the different variants and seed viability and management strategies: “A Review of the Biology and Ecology of Three Invasive Perennials in New York State: Japanese Knotweed, Mugwort and Pale Swallow-wort” by Leslie A. Weston, Jacob N. Barney and Antonio DiTommaso.