Japanese knotweed and selling your home: what you need to know

For most people selling a home, Japanese knotweed is the last thing they want to think about. If it is on or near your property, though, it is worth knowing where you stand. Having it is not against the law. What matters is what you say about it when you sell.

Here we explain what the law says, what the sale form asks, and how to answer it honestly without storing up problems for later.

What has changed on the sale form?

When you sell your home, you fill in a form that tells your buyer what you know about the property. It is called the TA6. Since 30 March 2026, solicitors who belong to the Law Society's quality scheme for conveyancing have had to use a new version of it. The new form is shorter and easier to follow, and it makes clear that you can answer "not known" if you honestly do not know.

Japanese knotweed is one of the things the form asks about. It is also one of the most common reasons sellers face a claim long after they have moved out. In most cases, the problem is not the plant itself. It is the answer given about it.

Is it illegal to have Japanese knotweed in your garden?

No. You do not have to remove it from your own garden, and you do not have to tell your neighbours it is there.

There are three things the law does say:

• You must not plant it, or cause it to grow in the wild.
• You cannot put it in your garden waste bin, on the compost heap or in a skip. Knotweed, and any soil with its roots in, has to go to a licensed waste site.
• If you do nothing while it spreads, your local council can serve you with a notice.

For most sellers, though, none of this is what causes problems. The sale form is.

What does the form ask about knotweed?

The TA6 goes to your buyer's solicitor. It is not a legal requirement, but almost every home sale uses it, and your buyer is entitled to rely on what you say.

The form asks two things about knotweed:

• Is the property affected? You can answer "yes", "no" or "not known".
• Has there been a survey, or is there a plan in place to treat it?

The Law Society's guidance on the form admits this can be hard to answer. A property is usually treated as at risk if knotweed is growing on it, or within three metres of the boundary. Even if you cannot see anything, the roots can lie hidden in the soil. That is why many sellers answer "not known".

That is helpful. But it will not protect a seller who answers "no" when they should have known better.

Why can answering "no" be risky?

A case from 2023 shows what can go wrong. A buyer paid £700,000 for a house in south west London. The seller had answered "no" to the knotweed question. After moving in and clearing the garden, the buyer found knotweed growing behind a bush near the shed.

The seller said he honestly thought his answer was true, because the plant had been hidden. The judge did not accept this. Experts showed the knotweed had once been around two metres tall, and had been treated with weedkiller while he owned the house.

He was ordered to pay around £32,000 in compensation, to cover the drop in the home's value and the cost of digging the plant out. He also had to pay up to £95,000 towards the buyer's legal costs, on top of his own. In total, the bill came to roughly £200,000.

The lesson is simple. Answering "no" means you are stating there is no knotweed. If that turns out to be untrue, and your buyer relied on it, they may be able to bring a claim against you for giving them wrong information. That can happen years later; time limits vary, but a buyer will often have up to six years. Knotweed you had treated four years ago is not ancient history. It is something you know, and your buyer does not.

Is "not known" a safe answer?

If you honestly do not know, "not known" is the right answer. It leaves your buyer to look into it, usually by paying for a specialist survey. But it cannot be used to hide something you already know. If you have a receipt for knotweed treatment in a drawer, "not known" is not a neutral answer. It is a misleading one.

Two more things to bear in mind:

• Keep your answers up to date. If knotweed appears, or you find out something new, before contracts are exchanged, tell your solicitor straight away so they can let the buyer know.
• If you are selling on behalf of someone else, for example as an executor or under a power of attorney, you are still responsible for your answers, even if you have never been in the garden.

What if knotweed spreads into a neighbour's garden?

Knotweed near your boundary brings a second risk. If it spreads onto your neighbour's land, they could bring a claim against you.

In a 2018 case, the Court of Appeal said a neighbour does not have to wait for any damage before doing this. Roots creeping into their garden can be enough on their own, because they affect how the neighbour can use and enjoy their property. You can be held responsible once you know, or should know, about the risk and do nothing reasonable about it.

A 2024 Supreme Court case has since limited this. Knotweed had spread from council land into a man's garden years before he bought the house, and before the council was at fault. The court decided he could not claim for the lasting drop in his home's value, because that loss had already happened before the council was to blame. This makes claims about older spread harder to win.

For sellers, the advice stays the same. If knotweed on your land is heading next door, deal with it. Do not assume a neighbour's claim would fail just because of that case.

Will knotweed stop your buyer getting a mortgage?

Not necessarily. Many people think knotweed makes a home impossible to get a mortgage on. That is no longer true, and believing it could cost you a sale for no reason.

Since March 2022, surveyors have followed new rules from their professional body, RICS. The old "seven-metre rule" has gone. Instead, knotweed is put into one of four categories, A to D, based on the harm it is actually causing rather than how close it is.

Lenders usually only hold back part of the mortgage in the more serious cases, where the knotweed is damaging a building or stopping you from using the garden. Knotweed that can simply be seen in a neighbour's garden, within three metres of your boundary, does not usually cause a problem at all. Some lenders do have their own rules, though.

What should you do if knotweed is found during your sale?

It is natural to want to get rid of it quickly. But try not to dig it out or spray it yourself, and do not say nothing and hope for the best.

Instead:

• Get a survey from a specialist firm that belongs to the Property Care Association or the Invasive Non-Native Specialists Association.
• If it needs treating, ask for a written treatment plan with an insurance-backed guarantee. These usually last ten years and can be passed on to your buyer.

Handing this over with your TA6 can give your buyer and their lender the confidence to go ahead. You may need to talk about the price. But a home with knotweed that is being properly treated can still be sold. Knotweed that has been kept quiet is far more likely to end in a claim.

Selling a home affected by knotweed?

The knotweed question can look like a simple tick box. In fact, you are personally responsible for your answer, and your buyer can rely on it for years. A careless answer can cost far more than the knotweed itself.

If knotweed is, or might be, at the home you are selling, or you are not sure how to answer, it is worth getting advice before you sign and return the form. And if you are already facing a claim, from a buyer or a neighbour, we can help you understand where you stand and what you can do next.

If you would like to talk it through, please call us, email us or visit our contact page.

Our Litigation team advises clients across Norfolk, Suffolk and beyond. Every client gets a named lawyer who knows their case inside out. If you would like to speak to the team, please call 01502 532300 or email litassistants@nicholsonslaw.com.