Japanese Knotweed

Japanese Knotweed is one of the Global Invasive Species Database's 100 worst invaders. It grows in a wide variety of habitats and tolerates a wide range of adverse conditions such as deep shade, high temperatures, salinity, and drought. It grows in dense thickets that shade out neighbouring species and spreads readily via underground rhizomes. Once established, it generally takes great persistence and several years to eradicate. Japanese Knotweed is widespread on PEI.


Japanese Knotweed was originally imported from Japan to North America as an ornamental garden plant. Since its arrival it has spread throughout Canada. In PEI it can be spotted along trails, in gardens and along roads. Urban areas are especially prone to invasion by Japanese Knotweed.


Japanese Knotweed may be confused with Giant Knotweed, a relative that also grows in PEI. Here are some differences between the two and some distinguishing features of Japanese Knotweed that may help you positively identify it:

  • Leaves are much smaller than those of Giant knotweed
  • Semi-woody, bamboo-like stem that can be red-purple
  • 1-2m tall
  • Flowers are white-yellow and grow on small, branching, flowering stems
  • Blooms July-September
  • Leaves are oval with pointed tip and arranged alternately
  • Spreads by extensive root system
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