Japanese knotweed: Lancashire hotspots revealed - and what to do if you think you have the invasive plant
If left unmanaged, knotweed can cause damage to buildings, hinder property sales and lead to legal disputes if it spreads across property boundaries.
Environet has revealed Lancashire’s Japanese knotweed hotspots for 2026 based on verified sightings from its live online tracker, Exposed: The Japanese Knotweed Heatmap, highlighting where homeowners and buyers are most likely to encounter the invasive plant.
The invasive species of plant spreads rapidly and overwhelms other plants. It hibernates during the winter months before emerging when the ground temperature reaches around 4°c.
There are 8,795 verified sightings of knotweed across the county, equivalent to 7 incidents in every square mile, making Lancashire the 5th worst-affected location in England after Bristol, Merseyside, Greater London and Greater Manchester.
If left unmanaged, knotweed can cause damage to buildings, hinder property sales and lead to legal disputes if it spreads across property boundaries.
Research conducted by Environet in partnership with Censuswide in 2026 indicates that 7 per cent of the UK’s homes – more than 1.58 million properties – are impacted by the invasive plant.
Lancashire’s Top 10 Japanese knotweed hotspots are as follows:
Blackburn - 756 varied sightings
Preston - 673.
Darwen - 394.
Burnley - 393.
Chorley - 386.
Lancaster - 288.
Clitheroe - 282.
Accrington - 267.
Ormskirk - 252.
Rawtenstall - 166.
How to spot Japanese knotweed during summer
- Tall, upright canes which can reach 2 to 3 metres high.
- Dense clusters of stems emerge from a central crown in the ground.
- Large green shield-shaped leaves with a pointed tip grow alternately up the stem.
- By late summer, cone-shaped tassels of small creamy-white flowers emerge on the upper canopy.
Environet Director Emily Grant said: “Japanese knotweed is now firmly established right across the country, which means homeowners everywhere should know what to look for.
“My advice to anyone living or buying a home in a Japanese knotweed hotspot is to check your garden regularly during the growing season
“The earlier it’s spotted, the easier and cheaper it is to deal with. Acting quickly with professional advice will prevent it spreading further and help protect both your property and its value.”