Bromley is one of the worst places in London for Japanese Knotweed

As Japanese knotweed’s summer growth period draws to a close, invasive plant specialist Environet has analysed the latest data from its live online tracker to reveal this year’s Japanese Knotweed hotspots.

Populated with almost 58,000 known infestations of the UK’s most invasive plant and charting its spread across the country, Exposed: The Japanese Knotweed Heatmap alerts homeowners and homebuyers to the risk level in their area.

Bromley has been found to be the third worst place in London for Japanese Knotweed with a total of 86 infestations.

Spitalfields was found to have the most Japanese Knotweed, with 97 infestations.

Exposed: The Japanese Knotweed Heatmap (Image: Exposed: The Japanese Knotweed Heatmap)With a total of 3,423 known infestations across Greater London, there are 2.2 occurrences of Japanese knotweed in every 1 km².

Japanese knotweed usually emerges in March or April and grows rapidly to reach up to 2.5 metres in height by mid-summer.

It is identifiable by its hard, bamboo-like canes and distinctive shield-shaped bright green leaves which grow in a zigzag pattern along the stem.

Mature plants flower in August, becoming covered in clusters of delicate tasselled creamy-white flowers.

Knotweed does not produce viable seeds as all the plants in the UK are female, so it is usually spread accidentally through the movement of soil or gardening waste, or via rivers and streams when pieces of rhizome break off and take hold in new locations.

Tackling Japanese Knotweed costs the UK economy nearly £250 million a year and homeowners are one of the groups most at risk – not only from potential damage to their property, outbuildings and gardens, which can be costly to repair, but also from legal risks arising from encroachment or when properties are sold.

Whilst it isn’t illegal to have knotweed growing on your land, if it is allowed to cross a boundary into an adjacent property, legal disputes can arise between neighbours.

Similarly, when properties are sold, sellers are asked a direct question about whether knotweed is present, even if hidden beneath the ground or within 3 metres of the boundary, and those who fail to declare it can be sued by their buyer for misrepresentation.

Environet estimates that approximately 5% of homes across the UK are currently affected by Japanese knotweed, either directly or neighbouring an affected property, typically impacting property prices by around 5% - or up to 10% in severe cases.

Nic Seal, founder of Environet, said: “Vigilance is the best way to protect your property from the risks posed by Japanese knotweed.

"Make sure you know what knotweed looks like and how it differs from other common garden weeds like ivy and bindweed, so you can keep an eye out for it in your garden and neighbourhood.

"Knotweed is easily identifiable during summer, but as we head through the autumn and into winter, the above-ground growth dies back and it becomes much harder to spot.

"It’s also easier to conceal, so anyone viewing a property to buy should be extra careful.

“There are lots of horror stories out there but the with professional help, knotweed can be successfully treated and a property’s value can be largely restored.”