Bath has been identified as the worst hotspot for Japanese knotweed in Somerset during 2026. The historic city, a UNESCO World Heritage site, recorded 162 verified sightings of this invasive plant species so far this year. Known for damaging buildings and lowering property prices, Japanese knotweed remains a serious concern for homeowners.
Research by invasive plant specialists Environet highlighted additional hotspots in Portishead (41 sightings), Clevedon (30), Keynsham (25), and Weston-super-Mare (24).
Emily Grant, director of Environet, stressed the importance of vigilance: “Japanese knotweed is now firmly established across the country. Homeowners, especially those in known hotspots, need to regularly inspect their gardens during the growing season.”
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According to Grant, early detection is crucial. “At this time of year, mature knotweed can be easily identified by its bamboo-like stems and bright green, shield-shaped leaves that grow in a zig-zag pattern along the stem. The sooner you spot it, the easier and more affordable it is to manage. Getting professional advice quickly helps prevent further spread and protects your property’s value.”
Introduced to Britain during Victorian times, Japanese knotweed has spread nationwide through contaminated soil, waterways, and a history of industrial activity. It doesn’t spread by seed but reproduces through an extensive root system that can extend up to six metres underground. Even tiny root fragments can regrow into new plants, making eradication challenging.
For homeowners, Japanese knotweed is a costly issue. It can cause structural damage, complicate property sales, and even lead to legal disputes if it crosses property boundaries. Environet estimates that properties affected by knotweed typically lose about 5% of their value, which can amount to roughly £13,500 per home.
While Bath tops the list for sightings in Somerset, its status as the county’s most populous city partly explains the numbers. The heatmap generated by Environet shows Japanese knotweed is most prevalent in urban areas, with Bristol having the highest verified sightings in England.
Importantly, the problem extends beyond cities. The Isle of Man, Channel Islands, and Isle of Wight also rank highly for infestations.
Top Locations in Somerset by Verified Japanese Knotweed Sightings:
- Bath - 162
- Portishead - 41
- Clevedon - 30
- Keynsham - 25
- Weston-super-Mare - 24
Broader County Rankings by Total Incidences and Density:
- Bristol – 1,324 incidences (32.29 incidences per square mile)
- Merseyside – 3,393 incidences (13.45 per square mile)
- Greater London – 4,704 incidences (7.67 per square mile)
…and others follow.
If you suspect Japanese knotweed on or near your property, you can send a photo to Environet for free identification. Early detection can make all the difference in managing this invasive species before it causes serious damage.