Japanese knotweed: what it means when buying a house
Japanese knotweed is not illegal to have on your land and does not automatically stop a purchase. Read the seller's TA6 answers, look along the boundaries, and get a specialist inspection if in doubt. Where it affects the property, lenders usually want a professional management plan. A Doorstep Report has no knotweed data, so this guide is general help.
How to spot it
A Doorstep Report has no Japanese knotweed data. It cannot tell you whether a property or its neighbours are affected, and its silence on knotweed means nothing either way. This guide is general help, not a survey or legal advice.
| When | What to look for |
|---|---|
| Spring | Pink-red buds at ground level, then fast-growing reddish-purple shoots. |
| Summer | Hollow, bamboo-like stems with reddish-purple speckles, often about 2m tall. Spade-shaped leaves in a zig-zag along the stem. |
| Late summer to early autumn | Clusters of small creamy-white flowers near the stem tips. |
| Winter | Stems die back, often leaving dry brown canes. The rhizomes underground stay alive. |
Look along boundaries and behind sheds and garages. Several plants look similar, including Russian vine and Himalayan honeysuckle, so treat your own view as a reason to ask. A clear garden proves little, because rhizomes can lie dormant with nothing showing.
What the TA6 form asks
In England and Wales, sellers usually complete the Law Society's TA6 Property Information Form. Conveyancing Quality Scheme firms must use the 6th edition for matters instructed from 30 March 2026. It asks:
- Question 8.6: is the property affected by Japanese knotweed? The answers are Yes, No or Not known. If yes, is a management and treatment plan in place? The seller should supply the plan and any linked insurance cover.
- Question 8.7: has a knotweed survey been carried out? If yes, the seller should supply it.
Not known is a legitimate answer, because knotweed can be dormant, but it is not an all-clear. Ask what the seller has seen and whether the garden has ever been treated. A buyer who relies on a wrong answer may have a misrepresentation claim, so keep your copy. RICS notes that knotweed must still be declared on the TA6 at resale, even after treatment.
How RICS treats it
The RICS standard Japanese knotweed and residential property took effect in March 2022 and was reissued as a Professional Standard that October. It is still the edition RICS lists. It replaced the 2012 paper behind the old seven-metre rule and looks at actual impact, using 3 metres for knotweed on neighbouring land.
| Category | Situation | Expected lender approach |
|---|---|---|
| A: Action | Visible damage to a significant structure | Specialist inspection and works under a management plan with an insurance-backed guarantee, with a retention |
| B: Action | No such damage, but likely to prevent use of or restrict access to amenity space | As category A |
| C: Manage | On site, but not causing damage or restricting amenity | No remediation condition or retention |
| D: Report | Not on site, but on neighbouring land within 3m of the boundary | Reported. A mortgage condition only in exceptional circumstances |
RICS says knotweed rarely causes structural damage to substantial buildings such as homes, although it can damage lightweight structures, walls, paths and drains. Valuers report what is clearly visible, so a valuation or survey is not a specialist inspection. See property report vs survey.
Mortgage lenders
Each lender sets its own policy. The RICS categories are guidance, a lender's instructions take precedence, and some lenders do not make retentions. If knotweed is found:
- Tell your lender or broker early and ask what it will accept.
- Arrange an inspection by a member of a recognised trade body. RICS names the Property Care Association and the Invasive Non-Native Specialists Association.
- Get the Japanese Knotweed Management Plan in writing. RICS says most provide a guarantee, for at least five years after the work is completed. A separate insurance policy keeps it valid if the contractor stops trading. Check that it transfers to you.
- Factor in treatment costs and timescale. RICS says stigma can leave some effect on value at resale, so ask whether the price reflects this.
The legal position
- Having it on your land is not an offence, and you do not have to report it.
- You must stop it spreading off your property. Under the Wildlife and Countryside Act 1981, it is an offence to plant it or cause it to grow in the wild.
- Plant material and contaminated soil can be controlled waste, so anything removed must go to a suitably permitted site.
- Councils and police can issue Community Protection Notices where it harms others' quality of life.
- Neighbours can claim in private nuisance. In Williams v Network Rail (2018), the Court of Appeal held that rhizomes encroaching on a neighbour's land can be a nuisance because they harm its amenity, but that a fall in value alone is not.
- In Davies v Bridgend (2024), the Supreme Court refused damages for loss of value where the knotweed had reached the land before the council's breach began.
Scotland and Northern Ireland have their own rules and the TA6 does not apply there, though RICS says the essentials of control and disposal are broadly similar. Take legal advice on any dispute.
If you suspect it
- Do not cut, strim or dig it, because that can spread it.
- Take photos and tell your conveyancer before you exchange.
- Book a specialist inspection, ideally of the neighbouring boundary as well.
- If it is next door, find who owns the land. RICS notes an owner cannot force a neighbour to act without legal action, so lenders should not make that a condition.
Questions, answered
Can you get a mortgage on a house with Japanese knotweed?
Often, yes, but it depends on the lender and the RICS category. Where the knotweed is causing damage or restricting use of the land, expect to need a specialist plan with an insurance-backed guarantee.
Is it illegal to have Japanese knotweed in your garden?
No. It is not an offence to have it on your land, but you must stop it spreading. You can face legal action if it spreads to a neighbour's land or into the wild.
Does a seller have to tell you about Japanese knotweed?
In England and Wales, the TA6 form asks directly and the seller must answer honestly. Not known is an allowed answer, so a form alone does not settle the question.
Does a Doorstep Report check for Japanese knotweed?
No. A report has no knotweed data and nothing in it should be read as a finding either way. Use the TA6, your own inspection and a specialist instead.