October 10, 2023

The Impact of Japanese Knotweed on UK Property Owners

Japanese knotweed, known scientifically as Fallopia Japonica, has earned a formidable reputation within the United Kingdom. As an invasive and fast-growing plant, it poses a significant threat to the value, saleability, and structural integrity of properties. This article explores the various challenges that Japanese knotweed presents for property owners in the UK, the legal repercussions of its growth, and the potential solutions available.

The Intrusion of Japanese Knotweed

Japanese knotweed is one of four invasive knotweed plant species identified within the UK, with the others being Dwarf knotweed, Giant knotweed, and Bohemian (hybrid) knotweed. Renowned for its bamboo-like appearance and shovel-shaped leaves, Japanese knotweed has the capacity to grow in diverse soil conditions, especially in man-made habitats like roadsides, waste grounds, railway embankments, and spoil tips.

Identifying Japanese Knotweed

Recognising Japanese knotweed is crucial in preventing its spread. The Non-native Species Secretariat website provides a comprehensive description and photographs of Japanese knotweed, enabling property owners to identify this invasive plant.

The Dangers of Japanese Knotweed

Despite its seemingly harmless appearance, Japanese knotweed can inflict severe damage on properties, leading to a sharp decline in property value and saleability. Its rapid growth and extensive root system can cause structural damage, particularly to lightweight structures with shallow foundations, such as conservatories, garages, paths, drains, and boundary walls. Below, we delve into the specific damages caused by Japanese knotweed.

Impact on Property Structures

Japanese knotweed can infiltrate outbuilding foundations, particularly those with weak constructions. Its root system is capable of growing through paving, tarmac, building foundations, and flood defences. Such damaging effects can lead to a property devaluation of up to 15%.

Financial Consequences

Even in minor cases where Japanese knotweed does not inflict physical damage, homeowners will still bear the financial burden of plant removal. However, in severe cases, the plant can exploit weaknesses in structures, resulting in costly repairs in addition to the removal expenses.

Environmental Impact

Japanese knotweed poses a significant threat to native plants, which are less equipped to compete with this foreign element. Its rapid growth and spread can stifle the growth of other plants in the area. This environmental impact often gets overshadowed by the financial costs associated with treating this invasive plant.

The Spread of Japanese Knotweed

Japanese knotweed propagates through direct rhizome (root) growth and new plant growth from the parent plant’s stem and rhizome fragments. Alarmingly, a new plant can sprout from rhizome pieces as small as 1cm.

The Legal Implications of Japanese Knotweed

While it’s not illegal to have Japanese knotweed on your land, it can lead to legal disputes with neighbours if it spreads into their garden. Moreover, you could be held liable for any removal costs or damages caused. Furthermore, any failure to control the spread of Japanese knotweed could contravene the Anti-Social Behaviour, Crime and Policing Act 2014, potentially leading to the issue of Community Protection Notices by the police or local authority and ultimately, fines.

Japanese Knotweed and Property Value

The presence of Japanese knotweed can significantly impact a property’s value. In a typical case of Japanese knotweed discovery, the property’s value can diminish between 5-15%. This financial impact primarily arises due to the stigma associated with Japanese knotweed, as most buyers prefer properties without an infestation or history of Japanese knotweed.

Engaging Specialists for Japanese Knotweed Removal

Due to the challenges associated with the removal of Japanese knotweed, it’s advisable to hire specialists with the right skills and experience. These experts can employ various treatment methods, including spraying with approved herbicides, burying, or burning the plant.

The Role of Surveyors and Mortgage Lenders

Mortgage lenders often hesitate to lend money for properties with Japanese knotweed growth. However, this reluctance can be mitigated if the current owner provides written evidence of the ongoing treatment of the infestation. This evidence should ideally come from a member of the Property Care Association invasive weed group, along with a transferable insurance-backed guarantee lasting 5 to 10 years.

Shifting Perceptions: The Overblown Threat of Japanese Knotweed?

Despite the alarm surrounding Japanese knotweed, recent research suggests that the plant’s threat may be overstated. The Royal Institution of Chartered Surveyors (RICS) has drafted new guidelines that challenge the formerly accepted “seven-metre rule” and adopt a more nuanced, evidence-based approach. Such developments indicate a potential shift in perceptions concerning Japanese knotweed.

In Conclusion

While Japanese knotweed continues to pose challenges for property owners across the UK, a more measured understanding of its impact is emerging, and with it, the potential for more objective and effective management strategies. Knowledge, early identification, and prompt action remain critical in mitigating the damage caused by this invasive plant.