Identification of Japanese knotweed

Identification is normally a straightforward issue

Fallopia japonica (Japanese knotweed) is common throughout the British Isles. While it often grows in damp conditions, it may also be found on dry, droughty soils, in coastal marshland, railway ballast, derelict land and domestic gardens. We have found Japanese knotweed growing in all situations all over the country. It is probably true to say that if you are currently reading this in the British Isles there will be some knotweed within one mile of where you are now – possibly nearer.

  • Winter: Knotweed is an herbaceous perennial, each winter frosts kill off the above ground growth, leaving a dense area of dead stems. The stems are hollow, smooth and break easily. At the base of the stems there may also be crowns, from which many stems grow.
  • Spring: The knotweed will form brown buds at ground level, and then young red shoots start growing, typically in April or early May. These shoots may resemble asparagus and are approximately 2 to 3cm thick.
    Extremely rapid growth is the norm for Japanese knotweed and in the spring with favourable temperatures, growth of 300mm per week is common in established plants.
    Stems are hollow and alternately 'zig and zag' at each leaf node.
  • Summer and Autumn: From July to October the plant is normally at full height – between 2-3m depending upon local factors. In August and September attractive creamy white flowers are borne.

The first frosts will cause rapid dying back of the knotweed and only dead stems will be left above ground. Below surface level though, it is still very much alive...