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Japanese knotweed check

Check any UK property for Japanese knotweed. Searches open source records within a 5-mile radius of the property: knotweed can affect your mortgage, insurance, and legal obligations.

Data sourced from publicly reported sightings. Most infestations are recorded, but physical surveys are recommended for certainty, not all knotweed is reported.

Japanese knotweed FAQ

How accurate is this check?

This tool searches open source records of Japanese knotweed sightings within a 5-mile radius of the property. While the majority of infestations do get reported, particularly those flagged during surveys or by councils, some infestations are never formally recorded. A clear result is reassuring but does not replace a physical invasive plant survey.

Can Japanese knotweed stop me getting a mortgage?

Yes. Most high-street lenders will decline or restrict a mortgage if Japanese knotweed is present within 7 metres of the property boundary. Some lenders require a professional management plan and insurance-backed guarantee before proceeding.[2]

Does Japanese knotweed have to be disclosed when selling?

Yes: sellers must declare Japanese knotweed on the TA6 property information form. Failing to disclose known knotweed is a misrepresentation and can result in legal action after completion. Even if you treat it before sale, it must still be disclosed.[1]

How much does Japanese knotweed affect property value?

Studies suggest Japanese knotweed can reduce property value by 5–15%. Beyond the direct devaluation, it affects buyer confidence and can significantly narrow the pool of mortgage lenders, effectively reducing demand.

What does Japanese knotweed look like?

In spring it emerges as red/purple shoots. By summer it grows into dense bamboo-like canes up to 3m tall with large heart-shaped leaves and creamy-white flowers. It dies back in winter but the roots (rhizomes) can survive for decades and regrow from fragments as small as 1cm.

How is Japanese knotweed treated?

Professional treatment typically involves herbicide injection or spraying over 3–5 years, or physical excavation and removal (more expensive but faster). Costs range from £2,000 for small infestations to £20,000+ for large ones. Always use a Property Care Association (PCA) accredited contractor.

Sources

  1. [1] GOV.UK: Invasive Plant Obligations
  2. [2] RICS: Knotweed and Residential Property

Further reading

GOV.UK invasive plant obligations · RICS knotweed guidance

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What is a Japanese knotweed check?

A Japanese knotweed check looks up open source biological records within a radius of a specific property to determine whether the plant has been sighted nearby. Homedata searches the aggregated dataset, drawn from biological recording databases, and returns the number of sightings within 8 km (5 miles) and the distance to the nearest one. For mortgage and legal purposes, the key threshold is 7 metres from the property boundary.

Why Japanese knotweed matters when buying property

Japanese knotweed (Reynoutria japonica) is one of the most problematic plants in UK property transactions. It was introduced as an ornamental plant in the 19th century and has spread widely along river corridors, railways, and disturbed ground. Its rhizome (root) system can extend 3 metres deep and 7 metres horizontally from the visible plant, causing damage to foundations, drainage, and hard surfaces.

From a property transaction standpoint, there are three main concerns:

  1. Mortgage availability. Most high-street lenders treat knotweed within 7 metres of the property boundary as a risk. Some will decline the application outright; others require a professionally prepared management plan with an insurance-backed guarantee (IBG) from a Property Care Association (PCA) accredited contractor before they will proceed.
  2. Legal obligation to disclose. Sellers must declare known knotweed on the TA6 property information form. Failing to declare it is misrepresentation and can result in legal action after completion: even if the knotweed has been treated, it must still be disclosed.
  3. Valuation impact. Studies suggest knotweed within or close to the boundary can reduce property values by 5–15%. Beyond the direct discount, it narrows the buyer pool by restricting mortgage access.

What to do if knotweed is detected

A positive result from this tool indicates recorded sightings in the area: it does not mean knotweed is definitely on the property. The next step is always a physical inspection and, if the plant is confirmed, engagement with a PCA-accredited specialist. Treatment typically takes 3–5 years via herbicide injection, or physical removal (faster, but more expensive).

Data sourced from open biological recording databases under OGL. Last reviewed: May 2026.