What is Japanese knotweed? Can it damage your property value? How to control the garden pest

The seemingly innocuous weed can wipe thousands of pounds off your house price and get you an Asboif you let it escape to a neighbour's garden.
1/4
Alex Mitchell17 May 2019

Japanese knotweed has long been feared by property owners, and London is a hotspot.

In spring new shoots of the bamboo-like plant emerge and quickly reach a height of two metres.

The strong roots can rampage under fences, damage paths and patios and work their way inside the cavity walls of houses, even emerging two storeys up out of the chimney stack. Removing knotweed from the London Olympics site cost £70 million.

If you allow knotweed to escape from your garden into a neighbour’s you could be prosecuted, or given an Asbo for causing a nuisance. It gets even more problematic if you are moving house.

Bamboo-like: the invasive plant can knock thousands of pounds of your house prices
Alamy Stock Photo

If you have knotweed growing in your garden you must declare it if you sell and this is likely to reduce the value of your property.

Mortgage lenders will want an insurance-backed guarantee that the knotweed has been eradicated before agreeing funds to a potential buyer.

Nic Seal from Environet says: “Even when treated there’s still a risk valuers will say there is a residual diminution of the property of two to five per cent.”

The costs for knotweed removal in an average London garden, he says, are around £2,500 plus VAT to treat with herbicide and £5,000 to £10,000 to dig it out.

Earlier this year a Londoner was awarded costs and damages of tens of thousands of pounds against a chartered surveyor who didn't spot Japanese knotweed growing in their garden.

In a case which will have surveyors checking their botanical guide books for years to come, the owner sued not only for the cost of the removal of the invasive plant from their property but also of "making good" the garden and distress and inconvenience suffered.

The judge also took into account the diminution of value of the property.

The owner commissioned a full structural survey when purchasing a ground-floor flat in 2014. The survey made no mention of knotweed so the owner went ahead with the purchase.

But the following year, their gardener found signs of the plant.

Environet, a company specialising in knotweed removal, confirmed the plant was in three sites in the garden and had been there for at least three years. The owner paid the company to remove it, at a cost of more than £10,000.

Create a FREE account to continue reading

eros

Registration is a free and easy way to support our journalism.

Join our community where you can: comment on stories; sign up to newsletters; enter competitions and access content on our app.

Your email address

Must be at least 6 characters, include an upper and lower case character and a number

You must be at least 18 years old to create an account

* Required fields

Already have an account? SIGN IN

By clicking Create Account you confirm that your data has been entered correctly and you have read and agree to our Terms of use , Cookie policy and Privacy policy .

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

Thank you for registering

Please refresh the page or navigate to another page on the site to be automatically logged in