Bristol still by far the biggest knotweed capital

Issues with the Japanese knotweed are by far the most prevalent in Bristol, analysis from invasive plant specialist Environet shows.

In the city there are 33.91 incidences per mi², followed by Merseyside with 11.87 incidences per mi², Greater London with 7.74 per mi² and Lancashire with 7.25 per mi².

Bristol’s historical role as a busy port has made it a hotspot for the invasive species, which was introduced by ships returning from Japan in the 1800s.

Emily Grant, director of 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.”

Environet found 100,000 known incidences of knotweed, which can pose a serious problem for homeowners, with underground rhizomes that can grow up to 3 metres deep and spread up to 7 metres horizontally, emerging through cracks in concrete, tarmac driveways, pathways, drains and cavity walls.

While serious damage to property is rare, since mortgage lenders require knotweed to be dealt with when a property is sold, it can cause legal disputes between neighbours and reduce a property’s value by approximately 5%.

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