What is Japanese Knotweed?

Japanese knotweed, the common name for the invasive species Fallopia Japonica, is a large perennial plant that was brought to the UK as an ornamental addition to the country’s gardens. However, since then Japanese knotweed has shown itself to be disruptive and destructive with the ability to grow through tarmac, concrete and structural work, causing damage along the way.

History and Origins

Japanese knotweed was brought into the country from Japan in Victorian times as an ornamental plant.

People planted the pretty, white flowered plant in gardens and public spaces, including riverbanks and train line embankments but did not realise the devastation that it can cause.

Knotweed still exists in Japan but is kept in check by indigenous predators that have evolved in such a way that they prune the plant naturally, therefore infestations are not problematic. Trials to introduce these insects to the UK have so far failed owing to our different climate and ecosystem.

Effects and Consequences

Over the last 200 years, Japanese knotweed has developed into a nationwide problem. The total annual cost of Japanese knotweed to the British economy was estimated at £166 million in the last study (Williams et al, 2010), however we believe this is a vast underestimation because most of the parties affected by knotweed are not compelled or willing to talk about it.

Japanese knotweed can grow up to 40mm per day during peak times and there is estimated to be at least one infestation of the plant in every 10 km2 in the UK.

As well growing quickly, Japanese knotweed is a hardy plant. Less than 0.7g of rhizome (the subterranean stem of the plant) is needed for a new plant to grow and become an infestation. This means that there is a high risk of cross-contamination whenever Japanese knotweed is removed from a site.

If an infestation takes hold and is not managed effectively, Japanese knotweed can infiltrate pipe work, tarmac and even concrete.

Identifying Japanese Knotweed

If you find something in your garden that looks like the plants in the pictures below, give us a call and we will happily tell you what we think with no obligation. Do not try to cut it down, dig it up, spray it or treat it yourself – this may exacerbate the problem. Leave this to the professionals.





© 2014 National Knotweed Survey. All rights reserved. Privacy policy.