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japanese knotweed control

Understanding Japanese knotweed

Invasive plants on your property

It may be easy on the eye, but you won't be happy if you find Japanese knotweed (Fallopia japonica) growing on your property. Known for its ability to relentlessly overrun gardens, it requires a similarly committed determination to get rid of it as it is very resistant to removal by hand or by chemicals. It causes millions of pounds in damage to UK houses and public land each year and can have a significant impact on home insurance claims. Here's how to identify and get rid of this noxious pest.

Japanese knotweed leaves and stems

What is Japanese knotweed

It's a green-coloured plant with bamboo-like stems with distinctive purple flecks. Also known as Japanese bamboo, it was imported from East Asia in 1825 as an ornamental plant and has been a veritable thorn in the side of property owners ever since.

How to identify Japanese knotweed

Unless you're a gardening buff, Japanese knotweed can be hard to spot. It's a year-round nuisance and is common to all parts of the UK. There's no real way of preventing it, but there are some tell-tale signs you should look out for:

  • Colour. Normally lush green leaves similar to fresh mint.
  • Size. Its leaves are usually 10 to 15cm in length and the stems can reach up to 2.1 metres (7 feet). Correct identification is important as it can be easily confused with hybrid or giant knotweed which have larger leaves. 
  • Form. They have a flatter base than other types of knotweed - giving the leaves a shield-like shape. 
  • Stems. Usually brown with purple freckles and often in a zig-zag pattern. 
Why it's bad for your house

Given the right weather conditions, growth can be unstoppable. Unfortunately, this plant thrives in the UK climate which is why it's a homeowner's nightmare. 
It grows very quickly, sometimes up to 20cm in a day, and can break through bricks, tarmac and concrete, causing subsidence damage to your property. It could also lower the value of your home and affect your chances of selling as some lenders may refuse a mortgage if the destructive weed is found on your property. If not dealt with properly, it may also cause disputes between you and your neighbours. 
Japanese knotweed spreads via deeply penetrating, creeping roots, which have been known to reach 3 metres deep underground. Because of this, it contributes to the erosion of river banks, increasing the risk of flooding and damage to property. On the surface, it quickly outgrows other plants, blocking natural light and killing anything underneath. 

Is Japanese knotweed damage covered by your home insurance? 

That really comes down to your policy. You'll be hard pressed to find one that singles out Japanese knotweed damage as an insurance risk. But the plant and its effects are well known to insurers. In many policies, you may be able to claim for the cost of controlling the plant or repairing the damage it's caused to drains or foundations under a subsidence claim. However, you should check with your insurer if in any doubt about what you are covered for. If you do find the knotweed on your property, your best bet is to try and quickly remove it as any long term damage probably won't be covered by your home insurance.

Are there any exceptions where I won't be covered? 

Although extremely rare, there's still a grey area surrounding cases where the knotweed actually grows into your house – as this tends not to be covered by most household insurance policies. 
We understand that knotweed can appear as if from nowhere, and if you suspect you have it on your property or see it growing next door, it's in your best interests to let your insurer know as soon as possible. It's worth noting that some insurers may choose not to offer you a quote if you have knotweed and haven't made any attempts to treat it.

How can I treat it? 

Japanese knotweed removal can be expensive and although it's not illegal to have it on property, you should make every best effort to control it from spreading and becoming an issue in your neighbourhood. Professional removal and treatment can set you back around £1000. If you don't have that kind of money going spare, you may want to consider these cheaper methods in the short term:

  • Cutting it away seems to be the most logical step to take, however, unless you get to and remove the roots as well, it could prove a fruitless task. Although Japanese knotweed doesn't produce seeds, it can start to regrow from the tiniest network of stems and roots; causing it to spread quickly and easily.
  • Using bugs to remove the knotweed isn't as strange as it sounds. Nearly a decade ago aphalara itadori were introduced in the UK. Although not totally foolproof, these bugs (part of the psyllid family of plant lice) only eat Japanese knotweed. A temporary measure at best, using bugs can at least slow down the spread of the knotweed while you consider your options. 
  • Treating it with chemicals is probably the most effective way of getting rid of Japanese knotweed yourself. You should really ask a horticulturist about which approved herbicides are available and how to apply them too. It won't be a miracle quick fix, but in the long run – usually within 3 to 5 years – your property could be free of the Japanese plant. 

For further advice and top tips on the control of Japanese Knotweed and other invasive species, visit the Royal Horticultural Society.

What if my neighbour has it? 

Japanese knotweed is a nuisance plant and is very difficult to get rid of. Because it can spread from one property to another, you should suggest your neighbour gets professional advice and treatment to remove it. If they don't make any effort to control it, you can take up the issue with your local council. They then have the power to hand the owner of the property a community protection notice if they don't think enough has been done to get rid of the problem. 

If you're looking to add a little more protection for your home, why not take a peek at our buildings insurance options today.


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