Japanese knotweed wipes £11.8 billion off UK house prices

The blight of Japanese knotweed has wiped an estimated £11.8 billion off the current value of the UK housing market, as the invasive plant continues to spread across the country making homes more difficult to sell, according to new research from Environet UK, the invasive plant specialists.

Approximately 4% of homes are affected by Japanese knotweed, either directly or indirectly (i.e. neighbouring an affected property), impacting their value by an average of 5%. Consequently, approximately 890,000 households across the country are suffering a typical reduction in value of £13,200 due to knotweed, knocking £11.8 billion off the value of the nation’s homes.

In a bid to limit diminution in property values and manage the risk posed by the plant, buyers and sellers of affected properties are increasingly turning away from traditional herbicide treatments and opting for excavations, where the plant’s extensive rhizome system is dug out of the ground. According to Environet’s data, almost 70% of customers opted for excavation of Japanese knotweed during 2021, an increase of +10.6% on the previous year, while the proportion of herbicide treatments has declined by -17.7% over the same period. A decade ago, herbicide was by far the most popular way of dealing with knotweed on residential properties, but more potent herbicides were available at the time which have now been banned.

Removing the root system from the ground is the only way to deal with Japanese knotweed decisively with minimal chance of regrowth. Despite the lower costs, herbicide treatment is increasingly being recognised by homeowners as a control method, as although above-ground growth may disappear, the root system beneath the ground is often induced into dormancy meaning it’s capable of regrowing in the future – particularly if the ground is disturbed by landscaping or building work.

Guidance from The Royal Institute of Chartered Surveyors (RICS) relating to the assessment of Japanese knotweed is currently under consultation with amendments expected to be published next month. The draft guidance places a strong emphasis on ‘control’ of the plant through herbicide treatments, yet evidence suggests homeowners are already turning away from these methods in order to protect the value of their homes.

Environet Founder and MD Nic Seal said:

“With knotweed wiping £11.8 billion off UK house prices this year, preservation of property values is the top priority for most homeowners. Those selling property are legally required to declare if the property is or has been affected by Japanese knotweed, but if an infestation has been professionally excavated with an insurance-backed guarantee to satisfy mortgage lenders, it is possible to restore the property value to close to the original value.

“Herbicide treatment of knotweed has always been very popular due to the lower costs, but the message is getting through that it’s only a control method and won’t solve the problem definitively. Buyers are much more wary of buying a property which still has knotweed rhizome beneath the ground as there’s no way of knowing whether it’s completely dead. There’s also an environmental cost to using chemicals, which is of growing concern.”

Excavation costs can be reduced by opting for a combination treatment and removal method, DART™, which removes the bulk of the knotweed crowns and rhizome system, massively reducing the plant’s vigour and stimulating growth of any small pieces of remaining rhizome, making them more susceptible to herbicide treatment the following spring. The excavation element can be carried out during the winter months, allowing for full use of gardens during the summer.

Kindly shared by Environet UK

Main photo courtesy of Pixabay