Japanese knotweed: what is it, what does it look like- and hotspot areas in London

Homeowners and gardeners across the country have been on the look-out for Japanese knotweed after a homebuyer successfully sued the former owner of their property due to discovering large quantities of Japanese knotweed in the garden. Since 2013, it has been a legal requirement that new owners must be made aware if there is Japanese knotweed growing on the property.

In this most recent case, the vendor of the property was ordered by the court to pay the new homeowner £200,000 for failing to make them aware of the pest. Japanese knotweed is known to be one of the biggest headaches for gardeners as it grows at a rapid rate and can take over gardens and buildings.

Invasive plant specialist Environet states that Japanese knotweed can also block drains, destroy asphalt, collapse brick walls, damage cavity walls and lift patios, among other costly issues. Treating Japanese knotweed quickly is vital to stop the plant from spreading and there are many methods out there to help contain the pest.

The Royal Horticulture Society (RHS) defines Japanese Knotweed as “a weed that spreads rapidly. In winter the plant dies back to ground level but by 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 as it is very hard to remove by hand or eradicate with chemicals.”

But what does Japanese knotweed look like and where are the hotspot areas in London? Here’s everything you need to know.

What does Japanese knotweed look like?

The RHS state that Japanese knotweed has reddish/purple shoots which emerge in spring. These grow rapidly, producing in summer, dense stands of tall bamboo-like canes which grow to 2.1m (7ft) tall.  These canes have characteristic purple flecks, and produce branches from nodes along its length.

The leaves of Japanese knotweed are heart or shovel-shaped and can grow up to 14cm in length.The weed’s stems die back to ground level in winter, but the dry canes remain for several months or longer.

Japanese knotweed hotspot areas in London

There are many Japanese knotweed hotspots in London. According to Environet’s interactive knotweed map, locations including Kilburn, Brixton, Hampstead and Hornsey have over 200 occurrences within 4km.

The hotspot checker is updated using data collected from around the country. To check out where you live, enter your postcode on the Environet website.