Bath has been identified as the worst affected area in Somerset for Japanese knotweed this year, with 162 confirmed sightings so far in 2026. This invasive plant species is known for causing serious damage to buildings and can significantly reduce property values.
Invasive plant specialists Environet have also highlighted other hotspots across Somerset, including Portishead (41 sightings), Clevedon (30), Keynsham (25), and Weston-super-Mare (24).
Emily Grant, director of Environet, emphasizes the importance of vigilance: “Japanese knotweed is now firmly established right across the country. Homeowners in affected areas need to know how to identify it and regularly check their gardens during the growing season.”
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Spring is the ideal time to spot this plant. Grant explains, “Established Japanese knotweed can be identified by its hard, bamboo-like canes and bright green, shield-shaped leaves arranged in a zig-zag pattern along the stems. Early detection makes treatment easier and more affordable.”
Originally introduced to Britain in Victorian times, Japanese knotweed spreads mainly through contaminated soil and waterways. It does not reproduce by seed but can regrow from small fragments of its extensive root system, which can extend laterally up to six metres underground.
The presence of knotweed can lead to severe consequences for property owners, including structural damage, hindered sales, and legal disputes if it crosses property boundaries. Environet estimates that homes affected by knotweed may lose around 5% of their market value—equivalent to about £13,500 per property.
While Bath tops the list within Somerset, the city is also the most densely populated in the region, and Japanese knotweed is most prevalent in urban areas. Bristol, nearby, has the highest number of confirmed sightings in England.
The issue extends beyond major towns: the Isle of Man, Channel Islands, and Isle of Wight also rank among the top locations affected by knotweed.
For those concerned about potential infestations, Environet offers free identification services—simply email a photo of the suspected plant for expert confirmation. The full UK heatmap of knotweed sightings is available on Environet’s website.
Somerset Hotspots Ranked by Verified Japanese Knotweed Sightings in 2026:
- Bath – 162 sightings
- Portishead – 41
- Clevedon – 30
- Keynsham – 25
- Weston-super-Mare – 24
- Taunton – 16
- Winscombe – 14
- Cleeve – 12
- Wincanton – 12
- Batheaston – 12
- Bridgwater – 12
Top Counties and Incidence Rates (Sightings per mi²):
- Bristol: 1,324 sightings, 32.29 per mi²
- Merseyside: 3,393 sightings, 13.45 per mi²
- Greater London: 4,704 sightings, 7.67 per mi²
- Greater Manchester: 3,688 sightings, 7.49 per mi²
- Lancashire: 8,795 sightings, 7.00 per mi²
If you suspect Japanese knotweed on or near your property, take action quickly to mitigate damage and protect your home’s value.