Japanese Knotweed

What is Japanese Knotweed?

Japanese Knotweed was introduced into Britain in the 19th century as an ornamental plant. Over time it has become widespread in a range of habitats including roadsides, railway embankments, riverbanks and derelict buildings. The invasive root system and strong growth can out-compete native plants and animals, damage foundations, buildings, roads, paths, retaining walls and architectural sites. It can also reduce the capacity of channels in flood defenses to carry water.

Japanese knotweed, Reynoutria japonica (synomyns: Fallopia japonica and Polygonum cuspidatum) is the most widespread form of knotweed in the UK. Stems form a zig-zag growth pattern, with one stem shoot per node. The leaves are fairly smooth, mid-green in color, with a characteristic straight top edge, giving the leaf a shield or shovel-type shape.

Knotweed flowers are small creamy-white and form in loose clusters (panicles) in late summer or early autumn. All Japanese knotweed plants growing in the UK are female and therefore do not produce viable seeds.

Although it does not produce seeds, knotweed can grow from very small sections of rhizomes and under the provisions made within the Wildlife and Countryside Act 1981, it is an offence to cause Japanese Knotweed to grow in the wild. Much of its spread is probably via topsoil movement or construction traffic.

For more information about Japanese Knotweed click here for the Environment Agency website.