A map has revealed the areas in south west London with the highest numbers of Japanese Knotweed sightings, and parts of Balham and Streatham are among the highest.

Japanese Knotweed is an invasive non-native plant that can grow up to 7ft tall and root itself deep in the ground, which can affect the foundations of your home and make it difficult to sell.

According to the Property Care Association (PCA), Japanese Knotweed is becoming a “more viable” plant, with advice to homeowners to treat it to avoid implications on property structures.

Where is it most prevalent in south west London?

A Heatmap created by Environet UK, comprising of over 51,000 sightings of Japanese Knotweed in the UK and Europe, has revealed the south London areas where the plant has been sighted.

Your Local Guardian: Heatmap of Japanese knotweed in South LondonHeatmap of Japanese knotweed in South London (Image: Environet)

According to Environet UK, the Heatmap is based upon reported sightings, where some are verified, and some are not.

As Japanese Knotweed is underground during the winter months, it is also possible that some sightings have gone undetected.

Number of reported knotweed occurrences in south west London:

In south west London the areas with the highest numbers of knotweed sightings were in Balham with 361 and Streatham Hill with 352.

Parts of the neighbouring areas were also high on the list, with 325 reported sightings within a 4km radius of Wandsworth Common and 316 sightings within 4km of Clapham Common.

Here are the top ten figures:

  • 361 within 4km of Balham Station, SW12 9BW
  • 352 within 4km of Streatham Hill Station, SW2 4SA
  • 344 within 4km of Tooting Bec Station, SW17 7AA
  • 325 within 4km of Wandsworth Common, SW18 3RT
  • 316 within 4km of Clapham Common, SW4 9DE
  • 309 within 4km of Brixton Station, SW9 8HE
  • 290 within 4km of Stockwell Station, SW9 9AE
  • 287 within 4km of Clapham Junction Station, SW11 2QP
  • 247 within 4km of Norbury Station, SW16 4EJ
  • 243 within 4km of Wandsworth Town Station, SW18 1SN

How to spot it

Japanese Knotweed can be identified by its distinctive red stems in February, when it emerges with fleshy shoots and pinkish buds.

Your Local Guardian: It's important to recognise Japanese KnotweedIt's important to recognise Japanese Knotweed (Image: Property Care Association)

During the summer months these shoots grow rapidly into tall bamboo-like canes that can grow up to 7 ft tall with purple flecks.

According to the Royal Horticultural Society (RHS) the plant can also be distinguished by heart or shovel shaped leaves that grow up to 14cm in length.

Your Local Guardian: The shoots grow rapidly during the summerThe shoots grow rapidly during the summer (Image: Property Care Association)

Why is it a problem for property owners?

The issue posed by Japanese Knotweed is that it is particularly difficult to remove by hand or using domestic weed killers.

To remove Japanese Knotweed effectively, stronger specialist chemicals are needed, or specialist contractors.

Under the Wildlife and Countryside Act (1981) it is an offence to cause Japanese Knotweed to grow in the wild and anyone fly-tipping the perennial shrub can be prosecuted.

Homeowners looking to sell their properties are required to state if Japanese Knotweed is present on their property, through what is known as a TA6 form.

According to Daniel Docking, the PCA’s Invasive Weed Control Group technical manager, the current climate conditions could have a detrimental impact on native plant species.

Your Local Guardian: Daniel Docking, Invasive Weed Control Group Technical ManagerDaniel Docking, Invasive Weed Control Group Technical Manager (Image: PCA)

Daniel said: “We can still expect late season frosts and dry weather in March and April, but Japanese knotweed has already started to establish itself and the resilience of the plant will mean it is in a strong position to thrive.

“As Japanese knotweed becomes more visible, we encourage anyone with concerns about the plant to seek expert help.

“Advice sought quickly will help to control and manage the situation effectively.

“Japanese knotweed is tied to legislation, which means landowners have a responsibility to manage infestations responsibly.

“Our ICWG members have a range of options to treat infestations, so it’s essential to engage a competent Certificated Surveyors in Japanese knotweed (CSJK) who will have the specialist skills and knowledge to identify Japanese knotweed or any other invasive plants that may be present.”