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Japanese knotweed warning as map shows invasive plant is running riot in Bath

Japanese knotweed is rampant in Bath, a new heatmap has shown. There are roughly 76 infestations within a four-kilometre radius, making it the worst affected part of Somerset this spring.

It is the UK’s most invasive plant and, if you have it on your property, it can lower the value of your home by five per cent. Japanese knotweed can grow up through cracks in concrete, tarmac driveways, pathways, drains and cavity walls.

After Bath, Keynsham was the worst-affected area, with 65 infestations. Then came Radstock with 16, Weston-super-Mare with 15 and Warminster with seven. There are over 55,000 infestations nationwide.

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Japanese knotweed first arrived in UK in 1850 in a box of plant specimens delivered to Kew Gardens. Favored for its rapid growth and pretty heart-shaped leaves, it was quickly adopted by gardeners and horticulturalists who were oblivious to its invasive nature.

Knotweed hibernates over winter but in March or April, it begins to grow, with red or purple spear-like shoots emerging from the ground which quickly turn into lush green shrubs with pink-flecked stems and bamboo-like canes.

The roots can grow as deep as three meters and spread up to seven meters horizontally. While serious damage to property is rare thanks to regulation which requires knotweed to be dealt with when a property is sold to a buyer using a mortgage or if it encroaches across a garden boundary, it commonly impacts use of the garden, causes legal disputes between neighbours. and can impact a property’s value.

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Homeowners and buyers who are unsure whether a property is affected by knotweed can now call in help from a specially-trained trio of sniffer dogs, Mick, Mack and Buddy, who will search a property for the unique scent of the plant’s rhizome even where it’s dormant beneath the ground or has been deliberately concealed.

According to Environet, approximately five per cent of homes are currently affected by knotweed, either directly or indirectly. However, sales can proceed as long as a professional treatment plan is in place with an insurance-backed guarantee to satisfy mortgage lenders.



The map of Japanese knotweed density in Somerset

Nic Seal, founder and managing director of Environet, said: “Japanese knotweed tends to strike fear into the hearts of homeowners but as long as they’re aware of its presence and take action to remove it before it causes any serious damage or spreads to a neighbor’s property, there’s no reason to panic.

“By publishing the 2022 hotspots for Somerset we hope to raise awareness and encourage people in the area to be vigilant for signs of knotweed as the growing season takes off, so they can act quickly if needed. Anyone living near or moving to one of these hotspots would be wise to check their garden carefully, enter their postcode into Exposed to find out how many known occurrences are nearby and if in doubt, seek expert help.”

How to spot Japanese knotweed

  • Asparagus-like spears emerge from the ground in early spring and begin to sprout pale green leaves with distinctive pink veins
  • In May the plant starts to grow rapidly. The stems harden into bamboo-like structures and the leaves, which grow in a zigzag pattern up the stem, are lush, green and heart-shaped
  • By mid-summer, the plant grows at a rate of around 10cm per day, with mature plants forming dense stands two or three meters tall
  • In August the plant blooms, with small clusters of creamy white flowers appearing on the upper leaf axials.

If you think you have Japanese knotweed in your garden, you can find out more about what to do here.

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