What is Japanese Knotweed?
Japanese knotweed or (Fallopia Japonica) was introduced to Britain by the Victorians for its ornamental attractiveness. The leaves are a vibrant green heart shape and attractive small white flowers. The stems are bamboo like and often red/green in colour. It can grow up to 4m in height and will die back in the winter leaving blackened stalks.
Young growth Japanese Knotweed in Autumn
Why is it bad?
The plant has a lot of bad press and is considered to be invasive. It can grow up to 40mm a day. The World Conservation Union has this to say on the plant: ‘…Japanese knotweed is almost universally disliked. The most extreme situation is to be found in the UK, where the plant is famous for its ability to devalue the built environment. It is not uncommon for banks to refuse to lend money for the purchase of a house that has knotweed within a certain distance of its boundary and developers are very wary of sites where there is a suspicion of knotweed presence. Japanese knotweed is often an indicator of a poor social environment and of urban decay, so many groups have become involved in eradication / control campaigns. The media have taken a keen interest in the plant and every season this generates hundreds of articles. In the UK, local action groups have rallied around the knotweed case, such as the Cornwall Knotweed Forum and various invasive species forums have followed suit. ‘ The full publication can be found here.
In short, the plant is highly invasive and generally disliked by individuals, the media and perhaps most importantly, mortgage lenders who may not lend on a property with Japanese Knotweed. The annual cost of Japanese Knotweed to the built environment is considered to be around £150m (Williams et al. 2010). The World Conservation Union suggest that if all Knotweed were to be professionally removed in the UK the cost would be around £1.3 billion.
How do I get rid of Japanese Knotweed?
The most common means of removal is to use a weed-killer such as glyphosate but this often needs to be used over 3-4 growing seasons. The plant will also regrow after the first treatment but will look different and this regrowth also needs to be treated. Alternative ways to remove the plant include digging out all soil and disposing of it in accordance with the Environmental Protection Act 1990. Japanese Knotweed is a controlled waste and cannot simply be thrown away. As the treatments can take a few years to succeed, the cost is normally fairly high.
It is not illegal to have Japanese Knotweed in your garden and there is no comeback on an individual/s who sells a property with Japanese Knotweed present, particularly if they were unaware that the plant was there. Always have a survey undertaken by a competent Building Surveyor.