Japanese knotweed and the Schedule 9 offence

Having Japanese knotweed on your land is not an offence. Causing it to grow in the wild is. Section 14(2) of the Wildlife and Countryside Act 1981 makes it an offence to plant or otherwise cause to grow in the wild any plant listed in Part II of Schedule 9, and Japanese knotweed is on that list. For a landlord or investor the practical exposure is rarely the criminal offence itself. It is the waste duty of care during works, the nuisance claim from next door, and the lender who will not release funds without a treatment guarantee.

There is no statutory duty to eradicate knotweed from your own site. That surprises people who have been told otherwise by a contractor selling a removal package.

What the Schedule 9 offence covers

The wording that matters is "cause to grow in the wild". That captures:

• Moving contaminated soil from one part of a site to another where the plant then establishes.
• Tipping spoil containing rhizome on a verge, a bank or an adjoining field.
• Flailing or strimming a stand so that fragments are thrown onto land where it was not previously growing.
• Allowing contaminated arisings to leave the site in an uncovered lorry.

A rhizome fragment of a few centimetres can regenerate, so the offence is easier to commit through carelessness than through intent. Prosecutions can be brought in the magistrates court or on indictment, and the court can also consider the costs of remediation.

Alongside the criminal route, a council or the police can serve a community protection notice under the Anti-social Behaviour, Crime and Policing Act 2014 where an occupier's failure to control knotweed is having a detrimental effect on the quality of life of those nearby. Home Office guidance treats invasive non-native plants as within the scope of that power. Breach of a notice is itself an offence.

Identifying it and mapping the stand

Misidentification runs both ways, and both are expensive. Russian vine, bindweed, dogwood, lilac and Himalayan honeysuckle get mistaken for knotweed by inspection reports, and genuine stands get missed in winter when the canes have died back to brown hollow stems.

The identifying features are the hollow bamboo-like canes with purple speckling, the shield or shovel-shaped leaves set alternately in a zigzag along the stem, and the creamy white flower spikes in late summer. Below ground, the rhizome is orange inside when snapped.

Mapping matters as much as identification. A survey should record:

1. The stand extent, plotted on a scaled drawing with coordinates.
2. A buffer zone, commonly seven metres from the visible extent, within which rhizome may be present.
3. Any hard surfaces, drains, walls or services within or crossing the stand.
4. Whether the stand crosses a boundary, and in which direction it appears to be spreading.
5. Photographs with a scale and a date.

Where the stand runs up to a boundary you cannot enter, record what can be seen and say what cannot. Our note on assessing ecology without access to adjoining land covers the wording that keeps a report defensible.

Duties on owners, developers and contractors

An owner or occupier has no duty to remove knotweed from their own land. What they do have is exposure under the common law of private nuisance where the plant encroaches onto neighbouring land or interferes with the neighbour's enjoyment of it. The Court of Appeal in Williams v Network Rail Infrastructure confirmed that encroachment and interference can found a claim, and that reasonable treatment costs are recoverable. The Supreme Court in Davies v Bridgend County Borough Council then held that damages for residual diminution in value are not available where the reduction in value preceded the breach of duty.

For a developer or contractor the more immediate duties are:

• The waste duty of care under section 34 of the Environmental Protection Act 1990, which applies to every movement of contaminated soil.
• Health and safety obligations where herbicide is applied, which require a certificated operator and, near a watercourse, prior agreement with the Environment Agency.
• The section 14(2) offence, which a contractor commits in their own right rather than on the owner's behalf.

Write the method into the subcontract. A groundworks package priced without the knotweed method statement is a package that will spread it.

Treatment, excavation and burial

Four approaches are in general use, and the choice is driven by programme rather than by biology.

Herbicide is the least disruptive and the slowest. Glyphosate-based treatment applied in late summer, when the plant is translocating to the rhizome, over three or more seasons, with monitoring in the following years. It does not deliver a clean site for a lender in year one.

Excavation removes the problem in days and creates a waste problem the same afternoon. The excavation has to extend to the full depth and lateral spread of the rhizome, which is deeper and wider than the visible stand.

On-site burial and encapsulation are governed by the Environment Agency's published position on treating and disposing of invasive plants, which sets the depths, the membrane specification and the conditions on which burial can proceed without a bespoke permit. Read the current version before specifying anything, because the position statements are revised.

Waste classification and the duty of care

Soil, rhizome and plant material contaminated with knotweed is controlled waste. Everything that follows from that is procedural and unforgiving:

• Use a registered waste carrier and keep the waste transfer note or consignment note for the required retention period.
• Send it only to a permitted facility that accepts it. Not every landfill does, and the gate fee reflects that.
• Sheet the loads, and clean plant and boots before they leave the stand. Wheel washing at the site exit is the control that stops a roadside stand appearing next year.
• Keep a photographic record of the excavation extent against the mapped stand.

A Preliminary Ecological Appraisal will record the presence of the stand and recommend a method statement, and biosecurity controls sit alongside it, as set out in our note on biosecurity method statements. The detailed knotweed management plan itself is written by an invasive weed specialist and is not one of the report types PlanScope produces.

Management plans, guarantees and lenders

A management plan is a document with a defined structure: site description, mapped stand and buffer, the treatment method with product and timing, the exclusion zone controls, the monitoring regime and the verification criteria.

Lenders are the reason the plan takes the form it does. A mortgage valuer who records knotweed within seven metres of a habitable building will normally require a treatment plan backed by an insurance-backed guarantee from a member of a recognised trade body for invasive weed control, typically running for ten years. Without the guarantee the valuation is qualified and the lending is refused.

Two things follow for an investor. The guarantee is transferable in principle but the transfer has to be documented, so check it survives the sale. And a treatment plan without a guarantee, however well written, does not solve the lending problem.

On sale, the standard property information form used in conveyancing asks directly about Japanese knotweed. Answering "no" where a stand is present, or "not known" where it plainly is known, invites a misrepresentation claim years later. Disclose, attach the management plan and the guarantee, and price accordingly.

Conditions a council may impose

Knotweed is a material consideration where development could spread it, and councils deal with it by condition. Expect some combination of:

• No development to begin until an invasive species management plan has been submitted to and approved in writing by the authority.
• Development to be carried out in accordance with the approved plan.
• A verification report to be submitted before first occupation, confirming the works were carried out and setting out the monitoring still to run.
• Retention of the exclusion zone and protective fencing during construction.

The verification condition is the one that catches schemes out, because it has to be discharged before occupation and the monitoring often continues beyond practical completion. Deal with the sequencing at the application stage rather than in the last fortnight before handover.

This is general guidance, not legal advice. Liability under the Wildlife and Countryside Act 1981 and the waste regulations depends on the facts, so take advice from a qualified professional and check current Environment Agency guidance before moving contaminated material.

Browse all 66 PlanScope report types to see which ecological documents a site with invasive plants is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.