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Should I buy a house with Japanese knotweed?

Kim Staples
Written by  Kim Staples
Jonathan Leggett
Reviewed by  Jonathan Leggett
5 min read
Updated: 26 Apr 2024

Homebuyers’ surveys have a section dedicated to one particular triffid-like plant: Japanese knotweed. But what is it, and what does it mean for your potential new home?

What is Japanese knotweed?

Japanese knotweed – aka fallopia japonica or reynoutria japonica – is a plant native to Japan, China, and Korea.

It was brought to and planted in European gardens years ago because it’s a rather pretty bamboo-like plant. But unfortunately, it’s one of the world’s most invasive species, and is now controlled under UK law. This can present a few problems if you’re buying or selling a home that has Japanese knotweed.

You can recognise Japanese knotweed by its big, heart-shaped leaves, and tall stalks that look a little like bamboo with ‘knots’ along them, which have a pink or red tint. It casts strong roots in the ground and can grow over seven feet tall.

See a gallery and read more on the Royal Horticultural Society website.

Why is Japanese knotweed bad?

Japanese knotweed is invasive, fast growing, and very difficult to get rid of. And, worst of all, it can cause damage to your home and to the ground.

Its roots are large, strong, and grow very quickly – and where they spread out, they can damage walls, floors, foundations, and even roads. It also suppresses other plant life where it grows, which can be a problem for gardens and for basic biodiversity.

Most buildings are safe from damage, as are the kind of substantial foundations you find on a house. But Japanese knotweed can still cause problems for less robust structures and foundations, such as greenhouses, conservatories, boundary walls, garages, and sheds. All of which can be costly to deal with.

Thankfully, Japanese knotweed isn’t quite as dangerous as we once thought, so rules have relaxed a bit in recent years. But UK law still lays out how it must be controlled, as it’s still a weed known for being invasive and causing issues – not least because it’s so tough to remove.

See the full guidance and rules for Japanese knotweed on Gov.uk.

Should I buy a house that has Japanese knotweed?

Japanese knotweed isn’t a death sentence on a property. But the severity of its invasion can affect how likely you are to get a mortgage and a good rate on home insurance – or just cost you money down the road. It’s something to be aware of, and to understand what it might mean for your new property.

Sellers must disclose if there is a Japanese knotweed problem. And if there is, they must also provide a plan from a specialist detailing how bad it is and how it can be dealt with.

RICS, the organisation that sets the standards for home surveys, set out new guidance on how surveyors should report Japanese knotweed in 2022. It’s a sliding scale that tells you how bad the invasion is, and gives you (and mortgage lenders) an indication of how tough it might be to manage.

Your survey will categorise it in the following ways:

  • Management Category A: Action – Japanese knotweed is causing ‘visible material damage to a significant structure’

  • Management Category B: Action – Japanese knotweed is present on the property, and not currently causing damage, but is ‘likely to prevent use of or restrict access to amenity space’

  • Management Category C: Manage – Japanese knotweed is present, but isn’t currently causing damage or otherwise affecting the space

  • Management Category D: Report – Japanese knotweed is growing within three metres of the property

If the survey reports category A or B, lenders will be reluctant to offer a mortgage on the property until there is a plan in place to manage the infestation. The seller will need to arrange a specialist’s report.

Category C or D is less likely to affect your ability to get a mortgage. But you should still pay attention to what it says, and be prepared to tackle the problem.

Ask for your solicitor’s advice – you may be able to negotiate a lower price, or require that the Japanese knotweed is dealt with before you move in.

Remember that if it’s present on your property, you’re legally required to do what you can to keep it under control.

Can I sell my house if it has Japanese knotweed?

You can sell a house with Japanese knotweed without falling foul of the law. But you’ll need to disclose the problem as honestly as you can.

There’s a section on the TA6 form where you can fill this out.

A good course of action is to hire a specialist and get a full report and plan, detailing how bad the problem is and how it can be dealt with. Buyers will most likely require this in order to get a mortgage anyway (see the section above for more info).

An even better course of action is to go ahead and follow that plan in advance, to eradicate the Japanese knotweed as best you can before even putting your house on the market. This can be costly – usually between £950 and £4,000, depending on the scale of the problem – but can raise the value of your property overall.

How to get rid of Japanese knotweed

It’s best to call in the professionals to get some targeted help on getting rid of your Japanese knotweed.

It’s notoriously difficult to remove: weed killer alone barely touches it, and yanking it out of the ground won’t do much either as it’ll just grow back. Bear in mind that this a plant that’s been known to survive lava from volcanic eruptions – it’s a tough cookie.

Some methods that can work include using a glyphosate-based weedkiller, which needs to be re-applied at different stages of the plant’s growth.

You can also dig them out of the ground, but will likely need to dig quite deep and wide to get all the roots up.

And finally, you’re also required to dispose of it correctly. Japanese knotweed is controlled waste under UK law, meaning you’ll need to dispose of it at licensed landfill sites that can take it. Definitely don’t just put it in your normal household waste or green rubbish collection.

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