What is Japanese Knotweed?

Image of Knotweed
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Summer is finally here!  The grass is starting to grow along with some particularly naughty weeds, some of which can leave a financially bad taste to a home owner or neighbour.

What is Japanese Knotweed?

Japanese Knotweed is known as one of the worlds most invasive plants.  It has a root system (rhizome) of 3 metres underground and up to 7 metres above ground.  The aggressive growth of this plant can have 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 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 prevent the spread of invasive, non-native plants at present, but if you leave it to grow onto neighbouring property, you could be prosecuted for causing a private nuisance.

What does Japanese Knotweed look like?

Japanese Knotweed have bamboo like shoots (canes) that when matured, have a distinctive purple specked colour.  The leaves are heart/spade in shape, up to 14cm (5.5in) in length and in summer, the plant produces creamy white flowers from tiny spiky stems.

The mature rhizome (underground part of the plant) is dark brown and the underneath is orange or yellow.  A newly formed rhizome is white in colour.  If the rhizome is cut through when digging, the knots of the plant 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 tiny spiky 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.

Get the Experts in:  There are ways that you can tackle the problem yourself but if you are serious about getting rid of the problem, then you need to contact an expert.  The contractor should be a member of the PCA (Property Care Association).

Do it yourself:  If you are thinking of removing it yourself, remove it, dry it out and then burn it or bury it 5 metres deep.  Never place it in green waste.  Removal by digging it out is possible but regrowth will most likely reoccur unless you remove all of the root and check the area again over many seasons.

Try the following methods to rid your garden of this aggressive plant:

Roundup Tree Stump and Root Killer 250 ml Liquid Concentrate Weedkiller

Roundup Ultra 3000 1 Litre Concentrate Weedkiller

Bayer Garden 80550936 800ml Ready to Use Tough Rootkill

Doff Maxi Strength Glyphosate Weed Killer 250ml – Treats Up to 416m2

It’s a bug’s life: A little bug has been introduced to the UK (aphalara itadori) that eats Japanese knotweed.  Although not available at the moment, if it proves successful it will become available to gardeners.  Join our mailing list to be updated on this.