New heatmap shows where invasive Japanese knotweed is growing - as plant costs economy millions

The plant is spreading exponentially across Britain. Credit: PA

The top Japanese knotweed hotspots in England have been revealed in a new map, as the invasive species continues to spread across the country.

It is now prevalent across almost all regions - with large swathes of the South East known to house the plant.

The map, designed by Environet, shows that it has spread to almost all major towns and cities, with Southampton and Brighton among the most affected.

Japanese knotweed can grow up to 10 centimetres a day and can push through cavity walls, drains and cracks in concrete and it can be difficult to remove, and is thought to cost the economy millions every year.

Japanese Knotweed is the UK's most invasive plant. It has the ability to grow through walls, tarmac and concrete.

Where has Japanese Knotweed been spotted?

The plant has been seen almost everywhere, and is known to be spreading across large swathes of land.

Hampshire has some of the highest concentrations. With Aldershot and Winchester each reporting 29 infestations, whilst Andover had 24.

Southampton comes out on top in Hampshire, with 118 infestations reported in 2023 so far.

This is a stark contrast between runner-up Portsmouth, which only had 30 infestations.

In Sussex, Brighton had 58 reports for every 4km of land, whilst Eastbourne reported 71.

Concentrations are lower in Kent, with Maidstone and Canterbury both reporting around 30 infestations each.

In the Thames Valley Reading comes out on top, with 78 plans for every 4km of land.

The Isle of Wight also ranks highly, with 76 plants found within a few miles Shanklin.

Japanese knotweed is one of the plants that the AI is being taught to track Credit: Barry Batchelor/PA

Why is the plant so dangerous?

According to the Royal Horticultural Society (RHS) Japanese knotweed (Reynoutria japonica syn. Fallopia japonica) is dangerous for native plant life.

The weed spreads rapidly in the warmer months and in winter dies back to ground level.

From early summer the bamboo-like stems emerge from rhizomes deep underground to shoot to over 2.1m (7ft), suppressing all other plant growth.

Eradication requires determination, the RHS says, as it is very hard to remove by hand or eradicate with chemicals.

It has also been known to cause structural damage to properties – which can be expensive to rectify – and decrease their values substantially.

The heatmap charts Japanese knotweed sightings across the UK Credit: Environet

In February, the Government published its GB Invasive Non-native Species Strategy to provide a framework to minimise the risk of invasive species.

At the time, Defra head of GB Non-Native Secretariat, Niall Moore, said: “Invasive non-native species pose a serious threat to our natural environment and this Government is taking action through the recently launched GB Invasive Non-Native Species strategy, to protect our native animals and plants from INNS.”

He added: “It is vital that we work together with researchers, scientists and others, who are working to tackle INNS, to prevent their entry into and establishment in Great Britain and, when they do become established, to mitigate their negative impacts.”

Meet the dog-tective who's on a mission to root out Japanese knotweed

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