Buyers urged to be vigilant for signs of Japanese knotweed during winter

Knotweed is easier to miss before new growth emerges in early spring

Homebuyers viewing properties during the next three months should be extra watchful for signs of invasive Japanese knotweed, which has now died back and is easier for sellers to conceal or surveyors to miss, warns invasive plant specialist Environet.

Until new shoots emerge in March or April, risks are higher for homebuyers – particularly those who are tempted to cut corners in the rush to beat the Stamp Duty deadline on 31^st March 2025 when tax bills will go up.

Japanese knotweed’s above-ground growth has now died back and the leaves have fallen to the ground, leaving only dead canes remaining. It’s therefore easier for sellers to conceal the plant, despite the fact it is a legal requirement to declare if a property is affected by knotweed on the Law Society’s TA6 form when they sell. Those who answer dishonestly or who fail to carry out proper checks, ticking ‘No’ or ‘Not Known’ in response to the Japanese knotweed question, are putting themselves at risk of future litigation if it’s discovered post-sale.

Yet there are still hundreds of misrepresentation cases brought by disgruntled buyers every year in a bid to recover treatment costs, legal fees and – most significantly – diminution in the property’s value. Worryingly, the results of a 2024 YouGov survey indicated that 15% of sellers would choose not to disclose knotweed to buyers or take any action to remedy it before a sale.

Emily Grant, director of Environet, said:

“Every spring we are contacted by people who have bought properties over the winter and then received a nasty shock in spring when knotweed shoots have begun to emerge. As well as removing the dead canes and covering the crowns, we’ve seen cases where knotweed has been covered with decking, had a pathway or patio laid over it, or even a shed. One client only understood why the back garden of the home he had recently bought had been concreted over when knotweed shoots began to spring up around the edges.

“Knotweed cannot be killed by concreting over it, burning it or applying over the counter weedkiller. Unless it’s professionally excavated or herbicide-treated over several growing seasons, it will grow back each year.

“Buyers viewing properties at this time of year should check carefully for evidence of knotweed and ask their RICS surveyor to be extra vigilant for signs of concealment. If in doubt, commission a specialist to carry out a Japanese knotweed survey, backed by a warranty.”

Approximately 5% of UK properties are affected by Japanese knotweed, according to Environet’s research, but as long as a professional treatment plan is in place with an insurance-backed guarantee, most mortgage lenders will offer a loan and the transaction can go ahead.

There are cost-effective treatments that can be undertaken through the winter months, allowing gardens to be fully operational during summer. The DART™ method involves excavating the bulk of the knotweed rhizomes from the ground, reducing the plant’s vigour and stimulating growth, enabling any new shoots that emerge the following spring to be herbicide treated.

Top Tips: How to identify Japanese knotweed during winter

Tall, hollow canes with a rich chestnut brown colour usually remain standing unless cleared
Zig-zag shaped stems are still visible
For mature plants, the distinctive crowns similar to rhubarb remain on the surface of the soil
In early spring, red or purple asparagus-like shoots will grow, quickly forming into green bamboo-like stems.