Environet Releases Cornwall Knotweed Hotspot Data for 2025

Cornwall’s 2025 Hotspots Revealed as Peak Season Hits

With Japanese knotweed now in full growth mode, homeowners across Cornwall are being warned to check for infestations as the invasive plant reaches its seasonal peak.

Invasive plant specialists Environet have updated their interactive heatmap, which shows Cornwall now has 1,254 verified sightings of Japanese knotweed. That’s 0.91 occurrences in every square mile, ranking it the 17th worst affected county in England.

The free-to-use tracker, Exposed: The Japanese Knotweed Heatmap, highlights risk zones across the country, allowing users to enter a postcode and check how many known sightings are nearby. The colour-coded system helps homeowners understand the potential risk to their property or one they’re considering buying.

Top 10 Japanese Knotweed Hotspots in Cornwall

How It Spreads and Why It Matters

Japanese knotweed first arrived in the UK during the Victorian era in a shipment of plant specimens sent to Kew Gardens. Gardeners were unaware of its aggressive growth at the time, and it has since spread rapidly across the country.

The plant typically emerges in early spring and grows quickly into dense green shrubs with heart-shaped leaves and bamboo-like canes. Its underground rhizomes can reach depths of 3 metres and spread up to 7 metres horizontally, sometimes breaking through concrete, tarmac, drains and even walls.

While serious structural damage is rare, the presence of knotweed can still cause legal disputes, reduce property value by around 5%, and affect mortgage approvals. According to a 2023 DEFRA report, knotweed costs the UK economy nearly £250 million per year to manage.

Expert Advice from Environet

Emily Grant, Director at Environet, said:

“By mapping verified sightings, we’re helping people understand the level of risk in their local area and encouraging early identification and treatment.

“Vigilance is the best way to protect your property from Japanese knotweed, making sure you tackle it as early as possible before it becomes well established. At this time of year, knotweed is in full growth mode and easy to spot with its bright green heart-shaped leaves which grow in a zigzag pattern up the stems. Mature plants flower around August, when they produce clusters of tiny white blooms.

“If you do suspect you have knotweed on or near your property, you can email a photo to us at expert@environetuk.com and we’ll identify it for free. If it is knotweed, a survey will determine the extent of the infestation and the best way to treat it, whether that’s digging it out of the ground, herbicide treating it or a combination of both.

“Public engagement is key in the fight against knotweed, and by reporting new sightings homeowners can play an important role in controlling this invasive plant and protecting property values.”

Homebuyers Can Now Check Before They Buy

Earlier this year, Environet also launched KnotSure™, a new risk report for homebuyers. It gives properties a rating from High to Low risk based on the number of nearby knotweed cases within a 2.5-mile radius, helping people make more informed decisions when purchasing a home.

To check for sightings in your area or to report knotweed, visit the Exposed heatmap.