There has been a fair bit of discussion on the TV and in newspapers recently about the ‘threat of Japanese Knotweed’. It is not something that, in 17 years of surveying, I have ever come accross. I thought I would do a bit of research, and this is what I have found:-
Japanese Knotweed is a member of the Japonica family. It has heart shaped leaves, a bamboo like stem and white flower clusters which appear in the late summer or early autumn. The hollow stems die back in the winter. The plant spreads from Rhizomes (small underground nodules). The plant can grow as much as 10cm a day! and reach 3m in height.
Japanese Knotweed was introduced from the Far East in the 19th century but spread rapidly. It has no natural ‘predators’ in this country so control is chemical based. It’s rapid growth has been known to cause damage to building floors and walls.
It is not illegal to have Japanese Knotweed in your garden but if you allow it to spread, you could cause a legal nuisance (a civil offence) for which damages might be awarded by a Court. It is an offence to dispose of the plant other than in a specified manner (under the Environmental Protection Act 1990).
In most cases, Japanese Knotweed can be controlled straightforwardly in a residential environment but knowledge is key. Residential development sites do need to be cleared of the plant before development and the costs of this can be high.
The plant has been in the news recently because trials have started using a natural pest which slows the growth and spread of the plant. This pest has been tested on native plants and crops (87 in total) to make sure it does not cause knock on environmental issues. Trials are in their early stages but, if successful, will help to reduce the estimated £150million a year costs of removal and clearance in the uk.