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Beware the Japanese Knotweed!

Beware the Japanese Knotweed!

Indisputably the UK's most aggressive, destructive and invasive plant

Left untreated, Japanese Knotweed can seriously damage the structure of your house. It can cause small structures like sheds to collapse altogether. It will grow and grow underground and can cover the entire underside of your house. It’s a creeping menace, like something out of a horror film. You should keep an eye for Japanese knotweed growing on your property. The earlier you spot it, the cheaper and easier it may be to manage and remove it. The roots of Japanese Knotweed can grow through concrete foundations and brick walls. Properties with Japanese Knotweed can be extremely hard to buy and sell, because mortgage lenders generally won’t lend on a property if the survey reveals it’s growing.

How can I get rid of it?

You can get rid of it yourself, but it’s a constant headache. The roots of Japanese Knotweed can be dormant for many years before they start to grow, so it’s easy to miss. It’s pointless to just cut off the bits you can see. If you leave even the tiniest amount it is likely to grow back and cutting it can often stimulate quicker growth. It’s the rhizomes underground that are the problem, so cutting it won’t do anything to get rid of them. You can get eradicating sprays, one of the most effective type is a glyphosate-based weed killer.

You may be well advised to hire an expert to get rid of it for you – these professionals are the shiny heroic knights of this terrifying story. They’ll work their magic to get rid of the Japanese Knotweed permanently. If you use a professional, you can also get a guarantee. If you have a guarantee, the knotweed shouldn’t stop you from selling your house. It's not illegal to have Japanese knotweed growing in your garden, but you do have to stop it from spreading to other people’s gardens.

The cost of getting Japanese knotweed removed varies depending on the height of the weed and how far it has spread, but it can run into thousands of pounds. If you do hire a professional to remove it, be sure to get a guarantee.

Is it covered by buildings insurance?

Most buildings insurance policies don’t cover Japanese Knotweed, but it's a little more complicated than a yes or no answer. Depending on how much the knotweed has grown, you may or may not need to let your insurer know about it. But if you don't, and you need to make a claim because of it, your insurer might refuse to pay out if they don't think you've done enough to stop the plant from damaging your property.

Will Japanese Knotweed affect the value of my house?

Usually yes - especially if you don’t have a professional remove it and implement a plan to make sure it doesn’t come back. If you’re trying to sell your property without getting rid of the Japanese knotweed, you’ll probably only be able to sell to cash buyers and at a lower price, as most buyers will be unlikely to find a lender who will lend on the property. 

My neighbour has it. What can I expect them to do about it?  

Japanese Knotweed is proscribed under the Wildlife and Countryside Act 1981, making it an offence to allow the plant to spread. All parts of the plant, and any soil contaminated with the rhizome, are classified as "controlled waste" requiring all the "duty of care" requirements under the Environmental Protection Act 1990 to be met.

So, your neighbour has a legal obligation not to let it spread onto your property. But they don’t have to get rid of it on their own property. If you’re trying to sell your home, this can pose a problem, because a lender may not lend on your property until your neighbour’s knotweed is taken care of and there’s a plan in place to stop it growing back.  Although it shouldn’t really be up to you, you have more of a reason to get rid of it than the person whose property it’s growing on, so you could end up footing the bill!


Japanese Knotweed is dormant during the winter but springtime is just a couple of months away.

In Spring: Young red/purple asparagus like shoots appear which turn green as they age. Some plants leaf initially but can grow 50cm as a straight rod.

In Summer: These shoots turn into bamboo like hollow stems, often with regular swollen red joints & nodes. Stems can grow up to 3m in height. Leaves are lush green and heart shaped. 

In Autumn: Flowers bloom 80mm-120mm in long clusters of small green/white flowers. In late autumn flowers start to fall.

In Winter: Stems turn brittle and brown, leaves turn brown/yellow and eventually fall off. This usually starts to occur during the first frost.

Although thankfully Japanese Knotweed is not rife in the Taunton area, some years ago it was identified in the garden of a property we were marketing on the Blackdown Hills, causing the agreed sale to be aborted. Make no mistake, this botanic pest is a real and present danger which we should ignore at our peril!

By Chris Willey

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