KnotweediDJapanese knotweed statistics: the UK picture
The key figures on Japanese knotweed in one place - how widespread it is, what it costs, how it behaves, and what it does to property transactions. Compiled and sense-checked by PCA-accredited surveyors; sources at the bottom. Journalists and researchers are welcome to cite this page.
Compiled by Alexander White, PCA Certificated Japanese Knotweed Surveyor (CSJK) · Updated July 2026How widespread is it?
Every countyJapanese knotweed has been recorded across the UK, in every county and virtually every 10km grid square of the national biological records.Source: NBN Atlas distribution data
~4-5%of UK homes are estimated to be affected by knotweed, either on the property or nearby - roughly one in twenty transactions has to deal with it.Source: industry estimates (Environet / YouGov)
One female cloneGenetic studies indicate UK knotweed descends from a single introduced female plant - it spreads by rhizome fragment, not viable seed.Source: Hollingsworth & Bailey, 2000
1840sbrought to Britain as an ornamental garden plant by Victorian horticulturalists - prized, ironically, for how vigorously it grew.Source: Kew / horticultural records
What does it cost?
£166m+ a yearthe widely cited estimate of what knotweed costs the British economy annually in treatment and property impacts.Source: DEFRA-commissioned research, 2010
£1.5bn+the estimated cost of attempting complete national eradication - which is why policy focuses on control, not elimination.Source: DEFRA estimate
£2,500-£4,500 +VATtypical professional herbicide management programme for an established residential stand, over several seasons.Source: PCA-member pricing, incl. Southwest Knotweed
£5,000-£15,000+typical range for excavation and off-site removal, rising with stand size and access.Source: PCA-member pricing
~5-10%typical diminution in value claimed for affected properties, depending on severity, proximity and treatment status.Source: RICS guidance & industry practice
~£250+starting cost of a professional residential knotweed survey - the document lenders and buyers actually rely on.Source: industry pricing
How does it behave?
10cm/daypeak growth rate of spring shoots - among the fastest-growing plants in Britain.Source: RHS / field observation
2-3m tallheight of a mature stand by mid-summer, dying back to bare canes every winter.Source: RHS
3m deep, 7m widemaximum recorded rhizome extent - though most sits in the top metre, and research shows lateral spread rarely reaches that far.Source: Environment Agency guidance; AECOM/Leeds research
0.7ga fingernail-sized fragment of rhizome can regenerate a whole plant - the reason disturbing it usually spreads it.Source: peer-reviewed propagation studies
Property, mortgages and the law
- Most UK mortgage lenders will lend on an affected property where a professional treatment plan with an insurance-backed guarantee is in place - blanket refusals are largely a thing of the past. See knotweed & mortgages.
- Sellers in England and Wales must answer a direct knotweed question on the Law Society's TA6 Property Information Form; a wrong "No" has grounded misrepresentation claims, including a widely reported 2022 case where a seller's "No" cost them six figures in damages and costs. See declaring knotweed when selling.
- It is not illegal to have knotweed on your land. It is an offence under the Wildlife and Countryside Act 1981 to plant it or cause it to grow in the wild, and cut material is controlled waste under the Environmental Protection Act 1990. Spread onto a neighbour's land can amount to a private nuisance - a civil matter, as the Supreme Court's 2024 encroachment ruling in Davies v Bridgend explored. See knotweed and the law.
- Misidentification is rife: bindweed, dogwood, lilac and bamboo are routinely reported as knotweed - which is why a first check matters before panic or paperwork. Try the free checker.
Citing this page? You're welcome to use these figures with attribution:
Need a quote from a PCA-accredited surveyor for a story? Email contact@knotweedidentification.co.uk.
Source: KnotweediD, "Japanese Knotweed Statistics UK" - knotweedidentification.co.uk/japanese-knotweed-statistics.htmlNeed a quote from a PCA-accredited surveyor for a story? Email contact@knotweedidentification.co.uk.
Sources and notes
- NBN Atlas - national distribution records for Reynoutria japonica.
- DEFRA-commissioned research (2010) - annual economic cost estimate; DEFRA eradication-cost estimate.
- Environet / YouGov survey work - household prevalence estimates.
- Hollingsworth & Bailey (2000), Botanical Journal of the Linnean Society - clonal genetics of UK knotweed.
- Environment Agency knotweed management guidance - rhizome extent figures.
- AECOM / University of Leeds field research - lateral rhizome spread findings.
- RICS professional guidance on Japanese knotweed and residential valuation.
- Law Society TA6 Property Information Form; reported case law including Downing v Henderson (2022) and Davies v Bridgend County Borough Council (2024).
- PCA-member treatment pricing, including Southwest Knotweed's own survey and treatment work.
Figures are the most widely used public estimates at the time of writing and are periodically revised; where ranges exist we quote the commonly cited middle ground. Last reviewed July 2026.
This page is general information, not a survey or legal advice. For a property sale, mortgage application or dispute, always obtain a confirmed survey from a PCA-accredited Japanese knotweed specialist.