The short answer
Japanese knotweed is an invasive plant that can affect property value and mortgages, but it is rarely a disaster: it is treatable, it is not illegal to have, and a managed plan usually satisfies lenders. The most common questions concern the law, selling, mortgages, treatment and cost. This hub answers them briefly and links to the detailed guides for each topic.
This page gathers the questions people most often ask about Japanese knotweed and answers each one plainly, with a link to the fuller guide. It is general information drawn from Tier-1 sources — RICS, the PCA, the Environment Agency and gov.uk — and is not a substitute for a site-specific survey or legal advice.
Knotweed essentials at a glance
- Illegal to have? No — but you must not let it spread
- Treatable? Yes — herbicide or excavation
- Survey cost £150–£350
- Treatment cost £1,500–£3,000 (herbicide)
- Mortgageable? Usually, with a guaranteed plan
- Key accreditation PCA
Is Japanese knotweed illegal to have in my garden?
No. It is not an offence to have Japanese knotweed on your land. It is an offence under the Wildlife & Countryside Act 1981 to plant it or cause it to grow in the wild, and you can face action under the Anti-social Behaviour, Crime and Policing Act 2014 if you let it spread and affect others. See knotweed law.
Can I sell a house with knotweed?
Yes. You must disclose it on the TA6 property information form, but a documented treatment plan with an insurance-backed guarantee usually keeps a sale on track. See selling with knotweed.
Will it stop me getting a mortgage?
Not usually. Many lenders accept a property with knotweed where there is a survey, a management plan and an insurance-backed guarantee. Some apply a retention. See knotweed and mortgages.
How is it treated, and what does it cost?
The two routes are a herbicide programme (about £1,500–£3,000 over three seasons) or excavation (often £5,000–£15,000+). See treatment vs removal and how to kill knotweed.
How do I know it’s really knotweed?
Look for bamboo-like stems with purple speckles, shovel-shaped leaves in a zig-zag pattern and creamy flowers in late summer — but confirm with a specialist, as look-alikes are common. See how to identify knotweed.
| Question | Short answer |
|---|---|
| Is it illegal to have? | No, but you mustn’t spread it |
| Can I sell with it? | Yes, with disclosure and a plan |
| Mortgageable? | Usually, with a guarantee |
| Treatable? | Yes — herbicide or excavation |
What if it’s come from my neighbour?
If knotweed has encroached from adjoining land, you may have a claim for treatment costs, following Williams v Network Rail. See encroachment claims and neighbour disputes.
What should I do first?
Leave the stand undisturbed and book a survey. The report confirms the plant, assigns a RICS category and recommends a costed plan — the foundation for everything else, from selling to mortgaging.
Still have a question? Start with a survey
The quickest way to answer your specific question is a PCA-accredited survey — a written report with a RICS category and a clear recommendation for your property.
Frequently asked questions
Is Japanese knotweed illegal to have?
No — it is not illegal to have it, but you must not plant it in the wild or allow it to spread onto other land.
Can a house with knotweed be mortgaged?
Usually yes, where there is a survey, a management plan and an insurance-backed guarantee from a PCA-accredited firm.
How much does it cost to deal with knotweed?
A survey is around £150–£350; a herbicide programme £1,500–£3,000; excavation often £5,000–£15,000 or more.
What should I do if I find knotweed?
Leave it undisturbed and book a PCA-accredited survey; do not cut or dig it, as that can spread it and create regulated waste.
Sources & further reading
- RICS — Japanese Knotweed and Residential Property guidance note (2022)
- Property Care Association (PCA) — Invasive Weed Control Group
- GOV.UK — Prevent Japanese knotweed from spreading
- Wildlife & Countryside Act 1981 — section 14 and Schedule 9
- Williams v Network Rail Infrastructure Ltd (2018, Court of Appeal)
This guide is general information, not a site-specific survey or legal advice. Japanese knotweed treatment and removal should be assessed by a PCA-accredited specialist before you act.