What is Japanese Knotweed?

    Japanese Knotweed (Fallopia japonica) is an invasive perennial plant that can cause serious structural damage to buildings and significantly impact property values.

    Origins and History

    Japanese Knotweed is native to Japan, Taiwan, and northern China where it thrives on volcanic slopes. It was brought to Britain in the 1850s by the Victorian plant hunter Philipp Franz von Siebold, who sold it as an ornamental plant.

    Without its natural predators (insects and fungi that control it in Asia), the plant spread rapidly across the UK and is now found in every county, including throughout the Isle of Wight.

    Physical Characteristics

    Above Ground

    • Hollow, bamboo-like stems
    • Purple/red speckled canes
    • Heart-shaped leaves up to 20cm
    • Grows up to 3 metres tall
    • Cream/white flowers (Aug-Sept)

    Below Ground

    • Rhizome network up to 3m deep
    • Spreads 7m from visible plant
    • Can remain dormant for 20 years
    • 0.7g fragment can regrow
    • Breaks through concrete/tarmac

    Why is Japanese Knotweed a Problem?

    Japanese Knotweed is classified as one of the world's 100 worst invasive species. In the UK, it causes an estimated £166 million in damage annually. The problems include:

    • Structural damage: Roots can exploit cracks in foundations, drains, and walls
    • Property devaluation: Reduces values by 5-15% on average
    • Mortgage refusals: Many lenders won't lend on affected properties
    • Legal liability: You can be sued if it spreads to neighbours
    • Disposal costs: Must be disposed of as controlled waste

    Explore the services most Isle of Wight homeowners, buyers and landlords go to next: