Japanese Knotweed (Fallopia japonica) was introduced to the UK from Asia in the mid-nineteenth century as an ornamental plant. Japanese Knotweed is an extremely invasive perennial weed that forms dense stands of 2-3 metre tall, bamboo like canes during summer that die back in the autumn. The woody, dead stems persist throughout the winter and new shoots emerge in the spring forming dense thickets. Its vigorous growth and persistent leaf litter suppress competition from native flora and prevent seeds from germinating.

Once present at a site, Japanese Knotweed spreads very rapidly and soon forms large monoculture stands. Japanese Knotweed does not produce viable seeds in the UK so reproduction occurs vegetatively from underground rhizomes and new plants can grow up from very small fragments of existing plants. As a result Japanese Knotweed thrives on disturbance and has been spread by both natural means and human activity. Along watercourses riverbank erosion causes fragments of the plant to break off and disperse downstream to form new colonies.

In the past transportation of contaminated soil containing rhizome fragments and fly tipping of garden waste and have been a major cause of it’s spread. However the Environment Protection Act, 1990, places a duty of care to ensure that any wastes are disposed of safely.  The Wildlife and Countryside Act, 1981, also makes it an offence to "to plant or otherwise encourage" Japanese Knotweed.

Japanese Knotweed is now a very serious problem in a range of habitats as it can grow almost anywhere, particularly roadsides, riverbanks and derelict land. It causes physical damage to roads and property having the ability to grow through tarmac.  It also reduces biodiversity by shading out native vegetation and offering a poor habitat for native insects, birds and mammals none of which will eat it.

Click here for more information on controlling Japanese Knotweed.