Japanese Knotweed


Japanese Knotweed (Polygonum cuspidatum (formerly Fallopia japonica)) Buckwheat family

An herbaceous perennial that forms extremely dense stands, shading out native vegetation. Stems to 10 feet tall, hollow, bamboo-like with thickened nodes where the leaf stalks meet the stem. Reproduces from extensive spreading rhizomes or broken-off pieces of stem. Leaves broadly oval and up to 6 inches long. Has small white to greenish-white flowers that bloom in late August/September. Dies back, turning bright yellow before dropping leaves in the fall.

Clogs waterways and lowers quality of habitat for wildlife, fish, and invertebrates. Has displaced salmonberries along shorelines.

Not known to occur in the Kenai Peninsula but could likely thrive here. Grows in Kodiak and Southeast Alaska. Found on roadsides, stream banks, and beach meadows.

More information


Kenai Soil and Water Conservation District    Alaska Association of Conservation Districts UAF Cooperative Extension Service National Park Service U.S. Forest Service Kenai Peninsula Borough