How to Identify Japanese Knotweed

Japanese Knotweed (Fallopia Japonica) is the most invasive and destructive plant in the UK. Introduced as an ornamental plant in the 1850's it quickly became naturalised and was first identified as a threat in 1887. 

 
 
japanese knotweed

How to identify japanese knotweed

Japanese Knotweed dies back in winter leaving woody bamboo sticks. In spring and summer, bamboo like shoots grow up to 2.1m (7ft) tall. In Spring dark red shoots start to appear from the ground, and grow rapidly. Once stems are fully formed they become hollow and speckled. Leave protrude from the stems on alternate sides creating a zig-zag pattern. 

  • Bamboo-like stems
  • Leave from either side creating a zig-zag
  • Mature stems are hollow
  • Sprouts from ground in spring
  • 'Dies' in winter
 
Japanese Knotweed in a domestic lawn

identifying japanese knotweed leaves

The picture to the left shows mature Japanese Knotweed leaves. They are shield shaped and up to 14 cm long. Young leaves are rolled and dark red in colour. 

 
Japanese Knotweed Stalks

identifying japanese knotweed Stalks

In late summer and early autumn before the foliage dies back the Japanese Knotweed produces creamy-white flower tassles, up to 15cm long. The stems chnage throughout the seasons but can be identified as follows:

  • Bamboo-like stems
  • Leave from either side creating a zig-zag
  • Mature stems are hollow
  • Sprouts from ground in spring
  • 'Dies' in winter