Japanese Knotweed

Japanese Knotweed (Fallopia japonica var japonica, Reynoutria japonica or Polygonum cuspidatum) is a non-native invasive species of plant.

Ironically, it was introduced into South Wales as an ornamental garden plant in the mid-nineteenth century and now has spread across the UK, particularly along watercourses, transport routes and infested waste areas.

Specific problems caused by Japanese Knotweed are:

  • Damage to paving and tarmac areas
  • Damage to retaining wall structures
  • Damage to building foundations
  • Reduction in land values
  • Aesthetic issues

The Problem:

The rhizome system of Japanese Knotweed may extend to, and beyond, a depth of at least 2m and extend 7m laterally from a parent plant and, according to the advice of the Environment Agency, the area of infestation should be regarded as 7m horizontally from the nearest growth of Japanese Knotweed that can be seen.

To determine exactly how far the rhizomes have spread, one would need to dig a series of test pits and examine them carefully. In our experience the Environment Agency’s guidelines, of extending the probable area of contamination by 7 metres beyond any visible sightings gives a good general rule to work to.

Knotweed is a serious problem plant and any eradication program needs to be pursued with equal determination.