Japanese Knotweed
(Polygonum japonicum, syn. cuspidatum,
Fallopia japonica)

Japanese Knotweed

A horribly invasive, perennial weed that is so tough it has been known to push its way through tarmac! It is incredibly fast growing reaching 2m easily in a growing season. You can easily recognise this weed for its thick bamboo like stems and large heart-shaped leaves, white flowers appear from the leaf bases from July to October.

Under the 1981 Wildlife and Countryside Act, it is an offence in the UK to allow it to grow in the wild. Waste material should be disposed of according to the Environmental Protection Act 1990 (Duty of Care) Regulations.

Control

The main way to keep weeds under control is constant vigilance, never allowing the weed to flower or seed and mulching. Japanese Knotweed is very difficult to control.

  • The best way is to start by cutting it down at regular intervals. Begin by cutting down and burning all the visible plant. After this cut it down every two weeks in the first year until autumn when the growth stops. In the following years cut it down as you see it

  • Trying to dig out the plant is difficult as it has an extensive root structure and will root from the smallest portion left behind

  • Spraying with weedkiller will do the job if the weeds are in the garden border. Spray with a systemic weedkiller that is absorbed through the leaves of the plant and the active ingredient makes its way through the cells of the plant down to the root. It kills these first and then the foliage starts to die off

  • Mulching will help to eliminate light, which all green plants need to survive. There are several effective mulches that will act as a weed barrier; weed suppressing fabric, well-rotted manure or garden compost, bark, grass cuttings, gravel and even a thick layer of newspaper