Japanese Knotweed


Japanese knotweed seeds in October

Japanese knotweed is a perennial forb and is invasive. The stems are smooth, stout and swollen at joints — resembling bamboo — where the six inch leaf meets the stem. Leaves are oval to somewhat triangular and pointed at the tip. This shrub like plant can grow to over 10 feet tall. Small white sprays of flowers occur in summer, followed by small winged fruits (seeds) in autumn. Japanese knotweed seedlings are edible. According to Wildman Steve Brill, “You can eat Japanese knotweed shoots from mid-April to early May, before the plant gets tough and woody.”

Japanese knotweed juvenile end of April

Juvenile plants can be uprooted with a hand digging tool. But if the stem breaks off from the root with the root remaining in the ground the plant will regrow. To remove mature Japanese knotweed, use a Pulaski tool to dig out the entire plant, including roots and rhizomes. Since any portion of the root system not removed will potentially re-sprout, be prepared to remove it repeatedly during the growing season until the plant has exhausted its reserves. It is also likely that in the process of disturbing the soil new seeds will germinate new plants. 

Japanese knotweed in flower in late August

An alternate method for removing Japanese knotweed is to wait until August at or just before blooming  when the root is at its weakest and the stem doesn’t crush under pressure. Then uproot each plant with a weed wrench (alternatives are available online). All plant parts and seeds should be bagged, solarized and disposed of to prevent them from reestablishing. 

Check out Invasive Herbs and Disposal Options posts for additional information.

Save Native Plants…Remove Invasive Species