Lancashire Japanese knotweed hotspots 2023 revealed

As Japanese knotweed’s summer growth period draws to a close, the latest data from Environet show a live online tracker that has revealed this year’s hotspots for the invasive plant.

Knotweed is capable of smothering out plant life, leading to a domino effect that causes insects and birds to leave the area as well. 

Japanese knotweed grows very quickly and has been known to cause damage to building structures, by targeting weak points and attempting to break through them.

The figures show Blackburn is the second worst hit part of the county, with 541 reported infestations of the plant, behind only Preston which has 857.

Elsewhere in East Lancashire, Burnley ranked fourth with 310 reports, followed by Accrington (236), Rossendale (220), and Clitheroe (212).

Environet has collated almost 58,000 known infestations of the UK’s most invasive plant and charted its spread across the country, and these statistics aim to alert homeowners and homebuyers to the risk level in their local area.

An example of Japanese Knotweed in a garden (Image: Environet)

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.”

The Lancashire Japanese knotweed hotspots for 2023 are:

1. Preston - 857
2. Blackburn - 541
3. Chorley - 365
4. Burnley - 310
5. Accrington - 236
6. Rossendale - 220
7. Clitheroe - 212
8. Carnforth - 133
9. Ormskirk - 115
10. Lancaster - 91

With a total of 3,530 known infestations across Lancashire, there are 1.1 occurrences of Japanese knotweed in every square kilometre.

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.

The invasive plant (Image: PA)

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 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 five per cent of homes across the UK are currently affected by Japanese knotweed, either directly or neighbouring an affected property, typically impacting property prices by around five per cent - or up to 10 per cent in severe cases.