Cornwall’s Japanese knotweed hotspots for 2026 have been revealed

Cornwall’s Japanese knotweed hotspots for 2026 have been revealed (credit: Knotweed Services UK Ltd)

Cornwall’s Japanese knotweed hotspots for 2026 have been revealed, with Bodmin and Liskeard emerging as the Duchy’s most affected areas – each recording 69 verified sightings of the invasive plant.

The figures come from Environet’s live online tracker, Exposed: The Japanese Knotweed Heatmap, which confirmed reports from homeowners, public bodies and submissions via its ‘Add Sighting’ feature.

Across Cornwall, the heatmap shows 1,259 verified sightings equivalent to 0.9 incidents per square mile, highlighting the scale of the issue facing property owners.

Japanese knotweed, introduced to Britain as a Victorian ornamental plant, is now one of the UK’s most problematic invasive species. If left unmanaged, it can damage buildings, complicate property sales and spark legal disputes if it spreads across boundaries.

Research by Environet and Cenuswide suggests seven per cent of UK homes – more than 1.58 million properties – are affected, typically reducing property values by five per cent or £13,500 per home.

Cornwall’s Top 10 Japanese knotweed hotspots

Bodmin – 69 sightings
Liskeard – 69
Penzance – 57
Truro – 50
Helston – 42
Launceston – 42
Falmouth – 38
Redruth – 34
Camborne – 32
St Austell – 31

The plant’s spread across the UK has been fuelled by contaminated soil, waterways and more than a century of industrial activity and construction. Although knotweed does not reproduce by seed in Britain – all plants here are female – its root system can extend up to seven metres underground, and even tiny fragments of rhizome can regenerate into new plants.

After ash dieback, knotweed is the second most costly invasive non-native species in the UK, responsible for an estimated £246.5 million in annual economic costs, according to CABI.

Environet Director Emily Grant said homeowners should be vigilant, particularly in hotspot areas.

“Japanese knotweed is now firmly established right across the country, which means homeowners everywhere should know what to look for,” she said.

“My advice to anyone living, or buying a home in, a Japanese knotweed hotspot is to check your garden regularly during the growing season. At this time of year, an established knotweed plant can be identified quite easily by its hard bamboo-like canes and distinctive bright green shield-shaped leaves which grow in a zig-zag pattern along the stem.

“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.”