What is Japanese Knotweed?

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What is Japanese knotweed

Japanese knotweed is known as one of the world’s most invasive plants.  The roots (rhizomes) can grow to 2-3 metres in-depth, and 7 metres laterally.  The aggressive growth of this plant can have a devastating effect as it can grow through weak spots in concrete, cement, cavity walls, brick payment and tarmac.  If left untreated, it could cause subsidence to your home because it continually looks for a route to reach water and light.

If Japanese knotweed is discovered within the boundary of your home or the boundary of an adjoining property, you could have a very costly problem to deal with.  New legislation (an amendment to the Anti-Social Behaviour, Crime and Policing Act 2014) includes Japanese knotweed.  It is not a criminal offence to have it growing on your property (see: prevent the spread of invasive, non-native plants), however, it is a criminal offence to allow it to grow from your property into the wild or plant it in the wild.  You can, however, be privately prosecuted if you allow it to grow onto the neighbouring property (encroachment), under the tort of private nuisance.

What does Japanese knotweed look like?

Japanese knotweed has bamboo-like shoots (canes) that when matured, have a distinctive purple speckled colour.  The leaves are shield or shovel-shaped, up to 14cm (5.5in) in length and in summer, the plant produces creamy white flowers in loose clusters called panicles.

The mature rhizome (underground part of the plant) is dark brown and the inside is orange or yellow.  A newly formed rhizome is white in colour.  If the rhizome is cut through when digging, a small piece of rhizome (just 0.7g) can potentially become a new plant.

How does Japanese knotweed grow?

In early spring reddish shoots appear from the soil forming into canes.  As these grow, the leaves gradually bloom and turn a lush green colour.

By early summer the plant is fully grown and can be as high as 2.1 metres (7ft).  The canes mature and grow and by late summer the plant has zig-zag stems covered in creamy white flowers.  By winter the plant dies and turns brown and hollow.  These canes may remain standing throughout the winter and new canes may grow through them the following spring.

How to treat Japanese knotweed?

Japanese knotweed is classed as controlled waste under the Environmental Protection Act 1990 which means it must be disposed of at a licensed landfill site and removed by an accredited professional.

Get the Experts in:

If you believe your property has been affected by Japanese knotweed, you should use a company registered with the Property Care Association to remove it.  Click here to find an accredited professional.

If you are considering treating it yourself:

Don’t.  You need to use an accredited professional to remove Japanese knotweed.  Using a herbicide treatment will not completely remove it, it will still remain dormant in the earth.  You would not be able to build directly on the area where it was present as it could cause problems for your planned structure later on.

If you are selling your house or plan to do so in the future, you would need to divulge to a buyer through the property information form that your property has Japanese knotweed.  If you failed to do this and your buyer discovered it at a later date, you could be retrospectively sued for misrepresentation and have to pay for any damage to the property since the buyer bought it, plus any perceived diminution in value.

Our best guidance is to have a professional remove it completely.

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