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  • Writer's pictureCharles Riley BA(Hons) DipSurv AssocRICS VRS

Japanese Knotweed in the UK - Unraveling the Truth and Empowering Homeowners

Updated: Jul 16, 2023

- Brooks Surveyors

Japanese Knotweed on a UK riverbank in Bridgnorth
Japanese Knotweed - Bridgnorth

Japanese knotweed (JKW), scientifically known as Fallopia japonica, is a highly invasive plant species native to East Asia, specifically Japan, China, and Korea. It is a perennial herbaceous plant belonging to the buckwheat family (Polygonaceae). Japanese knotweed is renowned for its rapid growth, robust roots, and its ability to dominate ecosystems.

During the mid-19th century, Japanese knotweed was introduced to the United Kingdom. Philipp von Siebold, a Dutch physician and botanist, brought it to the country as an ornamental plant in the 1850s. Siebold acquired the plant from Japan and introduced it to the Royal Botanic Gardens at Kew in London. Initially, Japanese knotweed was valued for its attractive appearance and ornamental qualities. However, its invasive nature and capacity to spread quickly soon became evident, leading to significant challenges for native flora. As a result, Japanese knotweed has now become widely established and is considered one of the most problematic invasive plant species in the United Kingdom.

Japanese Knotweed on an industrial estate in Stourbridge
Japanese Knotweed - Stourbridge

The infamous reputation of Japanese knotweed has often been exaggerated in the media, with publications like The Daily Mail contributing to the misconceptions. The Daily Mail has reported stories related to Japanese knotweed, including instances where homeowners faced difficulties due to structural issues supposedly caused by the plant. These reports frequently highlight the challenges associated with eradicating Japanese knotweed, its potential impact on property values, and the legal obligations of homeowners to disclose its presence when selling a property. However, we now know that Japanese knotweed does not cause structural issues.

Nevertheless, for a significant period, guidance from the Royal Institution of Chartered Surveyors (RICS) and major lending institutions was extremely cautious regarding JKW. This resulted in many properties with Japanese knotweed within or near their boundaries being refused mortgage lending services, with costly eradication plans imposed on them. However, this situation has changed since the release of the latest guidance on Japanese knotweed published by RICS in January 2022 (Japanese knotweed and residential property). High street lenders quickly adopted this new guidance, enabling property buyers to obtain mortgages on properties with Japanese knotweed on or near the boundary.

The guidance document includes a useful flow chart (below) designed for surveyors conducting valuation inspections of properties in the UK. It recommends advising retention only if the plant is "preventing the use of or restricting access to amenity space." In simpler terms, this means that an eradication plan will only be necessary if the plant has completely taken over the garden, preventing or limiting its use as a recreational area.

Japanese knotweed and residential property RICS 2022
Japanese knotweed and residential property RICS 2022

The guidance still addresses the scenario where Japanese knotweed is believed to be causing structural damage to a property. However, we believe this section is included as a precautionary measure, as such cases have never been documented or have since been disproven. In reality, trees or large shrubs situated close to foundations are far more likely to cause structural damage, a common occurrence observed by residential surveyors.

The reason behind writing this blog is to address the fact that although this information is widely known within the surveying industry, the average homeowner remains cautious and largely unaware of the new guidance, which has been in effect for over a year. Japanese knotweed is no longer the threat it once was, and we aim to spread the word and provide buyers with the necessary information to make well-informed property decisions.

Bonus Photos:

Gaint Japanese Knotweed (Reynoutria sachalinensis) in Bridgnorth
Gaint Japanese Knotweed (Reynoutria sachalinensis) - Bridgnorth

Three invasive species living in harmony by a stream on an industrial estate in Stourbridge (JKW, Himalayan Balsam and Giant Hogweed)
Three invasive species living in harmony by a stream on an industrial estate in Stourbridge (From bottom left to top right; Giant Hogweed, Himalayan Balsam, JKW)


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