People have been told to be vigilant when buying or selling property after the launch of a new interactive map which shows just how close the infamous Japanese knotweed is.

The tool provides an interactive heatmap of Japanese knotweed sightings throughout the country.

The plant is an invasive weed that plagues gardens and land which could have a detrimental impact on homeowners.

READ ALSO: How to get rid of Japanese Knotweed and everything else you need to know

It grows four inches a day in hot weather, and its roots or rhizomes spread underground causing structural damage to buildings.

Nic Seal created the tool, called Exposed, and he 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.

He added: "Exposed will be a useful tool for those buying and selling property and local residents who want to be aware of infestations near their homes which could spread, putting their property at risk."


The heatmap shows 53 Japanese knotweed infestations within 4km of Bromley town centre's The Glades.

From Greenwich Observatory there are 88 infestations within the same distance.

The number from Bexley train station is lower with 23 infestations within a 4km radius.

However, from Lewisham Shopping Centre there are 122 Japanese knotweed infestations within a 4km radius.

The plant was brought to Europe from Japan by Phillipe von Siebold in 1829 and sold as an ornamental plant. It spread because bits would break off and it does not take much to start growing a new plant.

People can check whether an area is blighted by putting their postcode on the Exposed: The Japanese Knotweed Heatmap.

Hotspots are marked from yellow to red based on the seriousness of infestation.

People are encouraged to report infestations using the 'add sighting feature' by attaching an image of the plant before experts verify it.

Environment Agency tips

A combination of herbicide treatment and careful excavation should eventually remove the problem.

The most effective time to apply herbicides to Japanese knotweed is in late summer.

A qualified person should carry out the treatment and contractors must have a National Proficiency Tests Council (NPTC) certification.

Herbicide treatment may have to be used for at least three years before knotweed stops growing back.

Contact your council to see if it offers a collection service or have a list of sites which can accept Japanese knotweed waste.