Background of Japanese Knotweed

Japanese Knotweed is the most invasive plant in Britain. Introduced in the 1850's as an ornamental plant, it has spread throughout the UK and Europe. If left uncontrolled, it will damage drains, foundations, walls, tarmac and concrete surfaces and can spread rapidly to seriously degrade its local environment by smothering native plants whilst providing no habitat for native fauna.

Due to these environmental impacts, it is one of the only two plants (the other being Giant Hogweed), that it is an offence under the Wildlife and Countryside Act 1981 to plant or cause to grow in the wild. Under the Environmental Protecton Act; Duty of Care Regulations 1991, cut knotweed material and soil containing rhizomes must be disposed of as controlled waste if they are to be removed from their site of origin. Furthermore, allowing the plant to spread onto neighbouring land can result in litigation for damages.

Biology of Japanese Knotweed

Japanese Knotweed is a perennial plant, of which all colonies are a clone of the original plant; therefore all plants found in the UK and Europe are female. Without the presence of male plants, it is therefore unable to set viable seed. Propogation is by vegetative means alone, as little as one gram of rhizome or five grams of green stem material is enough to cause a new plant to grow. The rhizome network underground (a type of modified root system) may extend to a depth of up to 3-metres and 7-metres around the perimeter of the clump.

Japanese Knotweed dies back in late October each year, leaving only dead brown hollow canes as an above ground sign of its presence. In late March each Spring, the rhizome system starts to throw up new shoots which look like asparagus on emergence. These shoots grow rapidly, reaching 2 metres by the end of May and 3-4 metres by the end of June, which are identifiable by their bamboo like nature and fleshy green/red tinged colour. The leaves are light green and heart shaped and in late August, the plant produces clusters of small cream sterile flowers.