Japanese knotweed wipes an estimated £21.4 billion from the value of the UK housing market, according to new research.
More than 1.5 million homes in Britain are affected by the fast-growing plant – which can grow through asphalt, patios, cavity walls, drains and cracks in concrete – according to new research from invasive plant specialist Environet.
A survey of 2,000 householders conducted with Censuswide in January 2026 suggests 7% of the UK’s homes are impacted by knotweed.
Knotweed reduces sales value by an estimated 5%, according to Environet. Based on the £270,000 value of the average property according to the UK House Price Index (February 2026), that’s £13,500 per average home.
“For most people, their home is their biggest asset, yet over 1.5 million households are seeing their property value undermined by knotweed,” said Emily Grant, director at Environet.
“Despite the fact knotweed is now much better understood than it was a few years ago, and many people are now quite pragmatic about it, a significant proportion of buyers still won’t touch an affected property under any circumstance.
Andrew McColl, chairman of the Residential Property Surveyors Association (RPSA) said: “Discovering Japanese knotweed can have significant financial implications, as removal and management plans are often costly and may require anywhere from five to ten years to fully implement. By ensuring you have accurate information before exchanging contracts, you can better anticipate and mitigate these expenses and potential complications, particularly those that may arise when dealing with lenders.”
Japanese knotweed costs the UK economy over £245 million every year, according to a 2023 report by Centre for Agriculture and Bioscience International.
Data from Environet’s live Japanese knotweed heat map, Exposed, which is populated with over 100,000 known incidences of knotweed across the country, reveals that Bristol, Merseyside, Greater Manchester, Greater London and Lancashire are among the worst affected areas.
On average, there are 1.1 occurrences of knotweed per square mile of England, rising to 3.9 in Wales.
