New online map tracks Japanese knotweed infestations across Bromley, Bexley and Gravesend

PUBLISHED: 07:00 18 February 2019

The Exposed: Japanese knotweed heatmap in action.

The Exposed: Japanese knotweed heatmap in action.


A new online map has been launched, allowing homeowners to check for outbreaks of Japanese knotweed in their area, and it shows there are currently 53 infestations around Bromley, 22 in Bexley and five in Gravesend.

The Exposed: Japanese knotweed heatmap can be viewed at, and uses postcodes to let homeowners see just how big a problem the weed is near them.

The general public is encouraged to help populate the heatmap, which is the only live tool of its kind, by reporting knotweed infestations using the ‘Add Sighting’ feature and attaching a photograph of the plant so it can be verified by experts.

Introduced to the UK in the 1840s as an ornamental plant, Japanese knotweed now grows rampantly along railways, waterways, in parks and gardens and is notoriously difficult to treat. Its presence can prevent a mortgage lender approving a loan and therefore impact a property’s value by up to 10pc.

Described by the Environment Agency as “indisputably the UK’s most aggressive, destructive and invasive plant”, Japanese knotweed’s rapid spread across the UK has prompted a Parliamentary Inquiry into its impact on the built environment, which is expected to release its findings this spring.

Nic Seal, Founder and managing director of Environet, who created Exposed, said: “This heatmap will help us build a nationwide picture of the Japanese knotweed problem and give the general public the information they need to assess the risk in their local area.

“Greater London is a significant Japanese knotweed hotspot and Bromley is no exception. Exposed will be a useful tool for those buying and selling property in the town and local residents who want to be aware of infestations near their homes which could spread, putting their property at risk.”

So how can you identify Japanese knotweed?

Around April and May, red or purple asparagus-like shoots appear from the ground and grow rapidly, forming hard canes.

As the canes grow, heart-shaped leaves gradually unfurl and turn green.

The plant grows at the incredible rate of around 10cm a day from May until July, when it is fully grown and can stand up to 3 metres tall.

Knotweed blooms in late summer, when it becomes covered in tiny creamy-white flowers.

During the late autumn, the leaves fall and the canes turn brown and die, although they remain standing.

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