Japanese knotweed - What landowners need to know

Japanese knotweed - What landowners need to know

Towards a greener financial system

Why has the two-word name given to a species of plant, that was once prized when it was introduced to English gardens as an ornamental plant in the 19th century, come to strike fear in the hearts of property owners?

Research has shown that the risk of physical damage to property is no greater with Japanese knotweed than any other invasive plant or tree. Nonetheless, the existence of this plant on or near land continues to wreak havoc within the property industry, with potential consequences including claims in nuisance, adverse valuation implications and general disruption and delay to potential sales or lettings.

What is Japanese knotweed?

Japanese knotweed is a perennial plant that grows and spreads rapidly and is very difficult to get rid of. The main eradication options are excavation or multi-year treatment plans involving herbicides. Both are expensive and if not carried out correctly may not be permanent, leaving the landowner with an ongoing risk of the plant regrowing in future.

With the potential problems posed by Japanese knotweed, what can landowners do to offset the negative consequences that the presence of this plant can have on a proposed sale or purchase?

What steps should be taken when selling property which is affected by Japanese knotweed?

The responsibility for controlling Japanese knotweed will in most cases lie with the landowner. Landowners who are considering selling or letting their property may want to consider ordering a high-level Japanese knotweed survey, which should enable them to spot any potential problems and put themselves in a position to pre-empt any issues which may hold up the sale.

When selling or letting a property, the landowner will need to be careful when answering replies to pre-contract enquires. For residential property owners the standard enquiry form asks: “Is the property affected by Japanese knotweed?” The accompanying explanatory note gives guidance on how to check for the presence of knotweed, which is an open invitation for the seller to give a well-thought-out answer to this question. However, sellers must be wary of the consequences of giving inaccurate replies. The seller should not be tempted to treat this or any other enquiry casually, as this may potentially lead to a claim in misrepresentation. Earlier this year, a court awarded a buyer £200,000 in damages in a case where the seller had denied the existence of knotweed at the property. The property was sold for £700,000 so the sum awarded was a very significant proportion of the price.

Sellers of commercial properties are also typically asked to disclose whether the property has ever been affected by Japanese knotweed. As the government’s guidance also now contains a section detailing how to recognise knotweed and to stop it from spreading, pleading ignorance will rarely works as an excuse.

Whilst selling with Japanese knotweed is never easy, if a seller is proactive and straightforward in its dealings and the buyer takes a commercial approach – particularly where any knotweed has already been eradicated and guarantees are available - then a sale should still be able to proceed.

What are the issues for a buyer to consider?

Potential buyers should in turn carefully scrutinise replies to enquiries and survey reports to check if the existence of Japanese knotweed has been disclosed. It may be that the property was affected by Japanese knotweed in the past but at the time of the impending sale it has been successfully eradicated. In such circumstances a well-advised buyer should inspect any relevant specialist reports to ensure that they demonstrate a proper treatment plan and provide an appropriate guarantee. In most cases the guarantee will be assignable to the buyer, but this also needs to be checked and the assignment properly documented.

Is Japanese knotweed a concern even if I have no plans to sell?

All owners of land should take care to ensure that if Japanese knotweed is on their land, they do not allow it to spread to any neighbouring property as this could potentially lead to a claim in nuisance. There are recent examples of landowners being penalised by the courts where they have been found to have allowed Japanese knotweed to encroach onto neighbouring property. The key point here is that liability can accrue by inaction or omission, as well as by a positive act, where the landowner knows of the existence of the knotweed and fails to use reasonable means to eradicate it. 


Japanese knotweed remains a significant issue for property owners and practitioners to grapple with. Although it is rare for the plant to cause structural damage to property, several high-profile cases in the last few years have highlighted that the existence of the plant on or near to property continues to cause problems for landowners, both in nuisance claims and providing sufficient comfort to a buyer when it comes to selling property.

The issues regarding Japanese knotweed are complex and the case law in this area is steadily building. With professional advice knotweed can be dealt with and the value of property preserved. If you have any questions on the above or require advice in this area, please contact our real estate team.

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