Estate agents are all too aware of the potential problems caused by invasive plant species such as Japanese Knotweed, with a number of sales falling through over the years as a result of the much-feared visitor to our gardens.

It was estimated last year that Japanese knotweed had wiped an estimated £11.8bn off the value of the UK housing market, as the invasive plant continues to spread across the country making homes more difficult to sell.

Last week it emerged that a property owner who sold his home with Japanese knotweed in the garden has been landed with a legal bill for £200,000 after being sued by the purchaser.

When Jeremy Henderson sold a three-bedroom house in Raynes Park, London, for £700,000 in 2018 he declared there was no knotweed present. But after the buyer, Jonathan Downing, completed the purchase he discovered the invasive plant growing behind a garden shed.

Downing sued Henderson over allegations that he misrepresented the state of the property before purchase.

With that thorny issue in mind, compliance officer at The Guild of Property Professionals, Paul Offley, says that the case is a stark reminder to agents that they need to remain vigilant and carry out a through inspection of each property they list for the invasive species.

He adds that Japanese knotweed is very difficult and expensive to get rid of and can cause costly damage to a building’s structure. While it may look small, the plant is capable of pushing its way through expansion joints, cavity walls and any weaknesses it finds within the structure of the home.

He commented: “Agents must always ensure that there is a question sent to the seller or the landlord asking if they are aware of the presence of Japanese knotweed in the property or within the area of the property. There should be the option the seller or landlord to answer either yes, no, or not known. It is imperative that the seller or landlord is made aware of the fact that if they tick ‘no’, when they know the property is affected, it is possible for this to be proven by a buyer and they could be sued for misrepresentation.

“Adding another skill to the list a property professional requires, Offley adds that agents should also be vigilant when walking around the garden to identify any suspicious looking plants. “There are various images available via the internet, but leaves tend to be shovel shaped and turn yellow in November and have creamy white and small flowers from August to mid-September – so agents should brush up on their Alan Titchmarsh skills.”

According to Offley, provided an agent stresses the importance of this to their client, and all the other topics on a Property Information Questionnaire (PIQ) ensure information is provided and they remain vigilant, then they are doing all they can to provide accurate information for potential buyers.

Adam Brindle, CEO and founder of Japanese Knotweed Specialists, last year offered the following advice when it comes to Japanese knotweed, which he says is present in almost every 10sq km of the UK, and continues to spread and crop up in new places every day.

When to Spot Japanese Knotweed

Identifying Japanese knotweed during winter and autumn is much harder as it loses its trademark heart shaped leaves and gentle white flowers. During winter and autumn, Japanese knotweed becomes nothing more than brittle canes above the ground, but below ground, the rhizome system continues to spread.

When it gets to growing season, which often begins in March or April, Japanese knotweed can grow up to 10cm a day. It will shoot out heart shaped, medium size leaves which are a lighter green in colour through its branches. In late August to October, gentle shoots of white flowers appear, which are very small and are stacked like a foxglove.

How To Spot Japanese Knotweed

Japanese knotweed can grow pretty much anywhere. It can grow through walls, pavements and even through the foundations of homes. You can find it in gardens, public land, building sites and even on the side of railway banks.

To spot Japanese knotweed, you should look for the heart shaped leaves and white flowers in late August to October. If you have a keen eye, in March you may be able to spot the reddish shoots that appear through the ground. However, a RICS survey or a dog survey will correctly identify knotweed throughout the year and confirm any suspicions you may have.

Why It’s Important to Spot Japanese Knotweed

Japanese knotweed causes a multitude of problems. It can affect the progress of building works, cause issues with mortgage applications, and even leave a home with up to 25% reduced value if it grows through the foundations. Japanese knotweed will also take over a garden, outgrowing all other plants in some cases.

It is important to consider the impact that Japanese knotweed can have on a building, especially if you are considering selling a home soon. While the guidance has recently been updated to help house sales go through, there is still reservation by many homebuyers to take on a home with an infestation.

There’s also legislation under the Anti-social Behaviour, Crime and Policing Act that specifically refers to a landowner who allows (whether intentionally or a lack of due care) Japanese knotweed to spread onto neighbouring land. And, allowing Japanese knotweed to grow in the wild or planting Japanese knotweed will find a homeowner guilty under the Wildlife and Countryside Act of 1981, liable for a fine up to £5,000.