Japanese knotweed

Property owners who fail to treat Japanese knotweed could face severe penalties.

Japanese knotweed is a problem you can’t ignore. Left unchecked, this fast-growing plant will take over your garden and possibly your neighbour’s too. In the worst cases, it can send shoots through walls, floors, Tarmac and drainage pipes, causing major damage. And failure to tackle it could mean prosecution and an expensive fine.

  • If you’re selling a property with knotweed, it could reduce the value by thousands of pounds. You could also face a hefty bill to eradicate it.
  • If you’re buying a property, you may find it hard to get a mortgage.
  • Recent court cases have seen property owners fined as much as £18,000 for failing to treat it.

In this guide we explain how to identify Japanese knotweed, the options for treating it, the law on knotweed infestations, and what to do if you are buying or selling a property with Japanese knotweed.

How to identify Japanese knotweed

Japanese knotweed

The plant dies down in winter, then in spring reddish shoots emerge at ground level from pinkish coloured buds. The shoots grow quickly – up to 10cm a day – to produce bamboo-like canes with distinctive purple flecks. These can reach more than 2m in height. The leaves are heart-shaped, up to 14cm long, and grow in a zig-zag pattern on the stem.

Left unchecked, the plant forms a dense canopy that starves other plants of light, so once established it can quickly take over a garden. In autumn, the decomposing leaves form an impenetrable mulch and stop other plants from germinating.

It does bear similarities to other plants and, particularly when dormant in winter, it can be hard to identify. There is a useful downloadable guide to identification on the gov.uk website – https://www.gov.uk/guidance/prevent-japanese-knotweed-from-spreading.

Japanese knotweed damage

2018 research found that Japanese knotweed rarely causes structural damage and that where it does, there is generally an existing defect. Despite this, horror stories abound and a quick internet search will bring up plenty of examples.

Even the smallest section of root will produce vigorous shoots and the underground rhizomes spread rapidly, as they make their way up into the light. A crack in masonry or in asphalt is the perfect opportunity for the plant and it has been known to find its way into the gap between cavity walls. In 2011 a newly built house in Hertfordshire lost more than £250,000 in value when  shoots were discovered growing up through the skirting boards.

Government guidance is that there is a risk of damage if there is an above-ground plant present within 7 metres of a building.

Japanese knotweed and the law

It is not illegal to have Japanese knotweed on your property as long as it is controlled and doesn’t spread outside your land.

It is an offence under the Wildlife and Countryside Act 1981 to cause Japanese knotweed to grow in the wild and the penalties are for doing so are serious. A magistrate’s court can impose a maximum fine of £5000 or a maximum prison sentence of six months, or both. A Crown Court can impose an unlimited fine or a maximum prison sentence of two years, or both.

In 2018 two court cases opened up the possibility of prosecutions under different legislation. Bristol City Council used the Anti-Social Behaviour Crime and Policing Act 2014 to enforce a Community Protection Notice (CPN) against a landowner for failing to address a Japanese Knotweed infestation. The landowner was ordered to put an eradication plan in place and also to pay an £18,000 fine.

A Japanese knotweed infestation can also be classed as common law nuisance where it’s deemed to cause unlawful interference with the use and enjoyment of someone else’s land. In 2018 Network Rail Infrastructure was successfully prosecuted by two homeowners who lived next to a railway line where the weed was prevalent.

How to treat Japanese knotweed

Treating an infestation yourself is not recommended as waste has to be disposed of very carefully. There is also a risk of spreading the plant further afield. There are many specialist firms who can tackle the problem, but it will be a lengthy process. It can also be expensive – eliminating the weed from the Olympic Park cost £70 million! While most gardens won’t be on the same scale as this, costs can still run to many thousands of pounds.

Treatment is usually by specialist herbicide or by excavation. Treatment normally needs to be repeated over a period of several years as the underground rhizome system is extensive and extremely tough. All waste material has to be burned to prevent it re-germinating as even a fingernail-sized piece of waste matter can re-grow. Another characteristic that makes it so hard to eliminate is the plant’s ability to lie dormant – for as long as 20 years! However, even if it’s difficult to destroy completely, it can be controlled and kept within manageable bounds.

The gov.uk website above has more information on the different treatment methods.

Selling a property with Japanese knotweed

At the outset, you must state whether Japanese knotweed is present when you complete the Seller’s Property Information Form (TA6) and if there is a management plan for eradicating it.

If you answer ‘no’ while knowing that there is an infestation, your buyer could make a claim for damages against you later on.

The presence of the weed is very likely to affect your ability to sell your property, particularly if you don’t have an eradication plan in place. Potential buyers will struggle to obtain a mortgage unless the mortgage lender is satisfied that the problem is under control. There is the option to sell to a cash buyer, but the value of your property is also likely to reduce significantly.

The best option may be to start an eradication plan and delay your sale – though this will of course not be possible for everyone.

Buying a property with Japanese knotweed

If you are using a mortgage to buy the property, your options will be limited by your mortgage lender’s policy on Japanese knotweed. Each mortgage lender has their own rules and some are more stringent than others. It will depend on the extent of the problem and the distance from the building.

Nationwide, for example, asks for an insurance backed 5 year warranty against the reappearance of the plant if it’s found within 7 metres of the property. HSBC will only lend if there is a treatment schedule and a completion certificate confirming that the weed has been eradicated. They also ask for a 10 year guarantee.

Your mortgage lender or broker will be able to advise you on your options.

If you are a cash buyer, you will have to decide whether you want to proceed with the purchase.

Our property lawyers will be happy to help with your queries regarding Japanese knotweed if you are buying or selling a property. Our Dispute Resolution team can also advise you if your property is affected by this problem and you wish to bring a case against someone else.

Contact us on 03300 562184 to speak to a property lawyer or 03300 562183 for the Dispute Resolution team.