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The Thug that could Scupper your Dream House – Japanese Knotweed

Japanese Knotweed is leading the pack of plant thugs threatening property transactions in the UK, and the discovery of Japanese Knotweed on a property can have a devastating effect.

When selling your house, you have an obligation to disclose the presence of knotweed during pre-contract enquiries made by your solicitor (TA6 Law Society form). And don’t think you can just tick the “don’t know” box. If you don’t know, you should find out.

Estate Agents also have an obligation under consumer protection regulations to advise prospective purchasers of any material facts that would affect their decision to buy. The guidance to these regulations identifies Japanese knotweed as being “material” so the estate agent must reveal its presence.
The lender’s valuation surveyor should also spot the presence of Japanese Knotweed, which would result in a recommendation not to lend.

Why Japanese Knotweed is feared so much.

1. It spreads by Rhizome and as little as 10mm of discarded rhizome can grow into a plant within 10 days.

2. It can grow up to 1 metre a month.

3. One plants roots (rhizomes) can grow 7 metres wide and 3 metres deep.

4. It can force its way through the smallest crack and roots will invade a property’s foundations, sewers, pipes, and ducts.

5. Treatment can be expensive, disruptive and take a long time.

The Cost

1. Big impact on land values.

2. £70 million was spent to clear Japanese Knotweed from 10 acres of the London Olympic site.

3. £2 million was the estimate to clear one development site in Cornwall ready for housing construction.

4. Some mortgage lenders will not lend against a property with a Japanese knotweed problem. Most will only lend if there is a plan in place to deal with it.

5. Insurers will not cover damage to property from Japanese Knotweed.

6. The Department of the Environment estimated the total cost of U.K. knotweed eradication would be £1.56 billion but it is now generally acknowledged that we will not be able to eradicate it but will have to manage it.

7. It must be treated as a Controlled Waste and can only be transported by a registered carrier to a registered place of disposal.

8. Unauthorised dumping of Japanese Knotweed can result in criminal prosecution, an unlimited fine and even imprisonment.

How to Deal with it.

Because of the difficulties involved in removing Japanese Knotweed it is best carried out by an approved contractor. Options include;

1. Treat chemically. It takes 3-5 years of repeat treatment to bring it under control. Spray in September so the treatment is drawn back into the rhizome as the foliage dies back. If sprayed in spring or summer it kills the top growth and can force the rhizome into dormancy. A rhizome can lie dormant for up to 30 years.

2. Dig up and transport to an approved landfill site. Every piece of rhizome must be removed because the smallest missed piece will start growing again. And remember, it can only be transported by a registered carrier of controlled waste.

3. Bury on site. It must be buried at least 5 metres deep and sealed within impermeable membrane.

4. Incinerate on site.

5. Biological controls are currently being trialled. This will not be a “silver bullet” but may help to control it.

You Must Not

1. Strim, mow or chip. If you do, this will just spread the problem further.

2. Compost it. It will just grow in the compost heap and don’t take Japanese Knotweed to recycling centres that receive garden waste as it will contaminate the compost. Plus, you will be breaking the law by transporting a controlled waste.

3. Don’t dump garden waste contaminated with Japanese Knotweed in the countryside. It can result in criminal prosecution, an unlimited fine and even imprisonment.

Japanese Knotweed is spreading but if you find it on your property, don’t panic. It can be dealt with. The main thing is not to ignore it. The earlier it is tackled, the easier and cheaper it will be to eradicate it.

This blog was provided by James Ferguson, the Director of X-Press Legal Services in Cornwall and Devon.

X-Press Legal Services publishes a website of free online legal guides for the public and small businesses. To find out more go to