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Buying Or Selling A Property Affected By Japanese Knotweed?

Tue 24 May 2016

We asked Nic Seal, Environmental Scientist and Managing Director of Environet UK Ltd to provide advice to buyers and sellers alike

Whereas rabbits are pre-programmed to eat grass and to go forth and multiply, Japanese knotweed DNA is hell bent on:

Destruction – it loves to damage human property, growing through asphalt, destroying walls and underground drains

Dominance – it spreads rapidly, being present in nearly every 10 sq km of the UK

Survival – it’s extremely difficult to kill, it laughs at DIY methods, and even shrugs off many so called “professional” attempts

That’s why the Environment Agency describe Japanese knotweed as “indisputably the UK’s most aggressive, destructive and invasive plant”. And yes, it can have a drastic effect on residential property sales so buyers and sellers of knotweed affected property should read on, or watch a short video at

What a buyer ought to know when buying a property with Japanese knotweed

The presence of knotweed on a property does not need to be a deal breaker but you do need to understand and be prepared for what you are taking on.

1) Identify whether knotweed is present on the property or in adjoining property

You need to identify whether the property is affected by Japanese knotweed, and, if it is, the scale of the problem. Don’t be fooled into thinking it’s a small problem if there is only a sprig or two, as it is the mass of underground rhizome system that is important. There is a short video at to help you correctly identify Japanese knotweed.

2) How to identify Japanese knotweed

Mature Japanese knotweed canes can be identified by their distinctive purple speckle and stand as high as three metres tall. This is when they are fully grown by early summer. The plants flower towards the end of summer and this consists of small white flowers, which are loved by insects for their nectar. In autumn, the leaves wither and fall off and the canes die back and go brown. The rhizome is the part of the plant that is submerged under the soil. It has a dark brown bark and under this external layer, it is orange or yellow.

3) Understand the liabilities that you’ll be taking on

You need to understand the liabilities the knotweed presents, because it will be your responsibility as the new owner. Has the knotweed encroached from or onto the land you are looking to acquire? If it has, then the first discussion you have with your new neighbours may not be as friendly as you had hoped. If the knotweed has encroached from land that will become yours then you are at risk of a legal claim in “private nuisance” from your new neighbour.

The knotweed may have caused damage to the building. It may not be immediately obvious, but knotweed can cause damage especially to underground elements such as drains.

4) Will the property provide suitable security for lending purposes?

You could experience difficulties securing a mortgage on the property if it’s affected by Japanese knotweed. Some lenders reject outright any property affected by knotweed. Others take a more pragmatic view and lend where the knotweed is being eradicated by a reputable firm and where appropriate insurance backed guarantees are provided.

5) Does anyone have a duty to disclose the presence of Japanese knotweed to the buyer?

The seller has an obligation to disclose the presence of knotweed during pre-contract enquiries made by your solicitor (TA6 Law Society form). However, at this stage you will have invested plenty of money, time and emotional energy, and to have the bad news dropped on your lap at the 11th hour will be unwelcome news.

The estate agent does have an obligation under consumer protection regulations to advise you of any material facts that would affect your decision to buy. The guidance to these regulations identifies Japanese knotweed as being “material” so assuming the estate agent is acting professionally you should be guarded against this eventuality.

And finally if neither seller nor estate agent disclose the presence of Japanese knotweed there’s a strong chance that your lender’s valuation surveyor will result in a recommendation “NOT TO LEND”.

6) If the property is identified as affected by Japanese knotweed should we pull out of the sale?

There is no simple answer to this, as it depends on numerous factors. What you need to do is understand what you are taking on and satisfy yourself that it’s reflected in the price you are paying.

Don’t fall into the trap of letting the seller “sort out” the knotweed problem. A cheap attempt at eradication with inadequate guarantees is unlikely to work. Insist that the work is carried out by a firm that you trust will do the job properly, otherwise walk away.

If you are buying and knotweed is found, get professional advice. You’ll need a survey and Management Plan report which will highlight all the issues, the costs as well as satisfying your lender.

What a seller ought to know when selling a property with Japanese knotweed

A property infested with Japanese knotweed can make it difficult to sell. Buyers would much prefer to buy a knotweed-free property than have to fork out considerable sums of cash to eradicate this highly invasive species.

This is where you as the seller need to make the most out of the situation, in order to make your property attractive to potential buyers.

1) What should you not do when it comes to selling a property with Japanese knotweed?

Intentional concealment is not a good answer! You need to be aware that the Law Society’s TA6 form now has a specific question relating to Japanese knotweed and if answered untruthfully during the conveyance process, a legal claim of misrepresentation could possibly be brought against you by the buyer.

If you do try and conceal the knotweed, there are now highly trained RICS Surveyors, whose task it is to spot knotweed and bring it to the attention of interested parties, especially the lender.

2) What is the correct way to go about removing Japanese knotweed and improving the chance of selling?

If time is available then commissioning a remediation firm to eradicate the knotweed and provide suitable guarantees will be advantageous. Don’t fall into the trap of DIY attempts. Be aware that inappropriate treatments, through the use of ‘off the shelf’ herbicides, can actually induce rhizome dormancy and make any subsequent treatment more difficult and costly. This may make it impossible to obtain an insurance backed guarantee, which will be required by any buyer requiring a mortgage.

It’s best to engage the services of a reputable knotweed specialist who can eradicate the knotweed and provide suitable insurance backed guarantees which will be acceptable to all lenders. And make sure that the guarantee can be assigned to your prospective purchaser.

3) How to get rid of Japanese knotweed

Getting rid of Japanese knotweed yourself is not easy and takes patience! The most popular technique is to use a glyphosate herbicide but this will require a high dosage and it will not be eradicated after just one dose. It will require repeated doses to completely rid your garden of Japanese knotweed. If you are diligent in ensuring you are not inadvertently spreading it across your lawn, repeated mowing can also deplete the plant until it withers back. It can also be dug out, but only if you are meticulous in ensuring that there are no traces left in the ground. In fact, the best way to rid your garden of Japanese knotweed is to combine all of the above methods.

4) Examples of Japanese knotweed damage to property

Japanese knotweed can cause serious structural damage to property. The rhizomes – the submerged part of the plant – can grow as deep as three metres underground and spread across an area as far as one hundred metres. As well as undermining concreted pathways and patios, it can also grow under foundations and affect the integrity of them.

This information can be found on

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