Growing season is underway for the UK’s most invasive plant, with nearly 60 infestations of Japanese knotweed recorded in Oxfordshire.

Japanese knotweed first arrived in UK in 1850 in a box of plant specimens delivered to Kew Gardens.

Gardeners and horticulturalists quickly favoured the plant, as it has pretty heart-shaped leaves and grows rapidly, but they were oblivious to its invasive nature.

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For homeowners, the plant can pose serious problems if left unchecked, with the potential to grow up through cracks in concrete, tarmac driveways, pathways, drains and cavity walls.

Witney Gazette: An example of Japanese knotweed. Picture: Environet UKAn example of Japanese knotweed. Picture: Environet UK

The roots can grow as deep as three metres and spread up to seven metres horizontally.

Serious damage to property, however, 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 by around 5 per cen.

Oxfordshire’s hotspots

A heat map has now revealed the Oxfordshire hotspots of the invasive plant.

Using data from its interactive online tracker, invasive plant specialist Environet UK has mapped the knotweed hotspots for spring 2022.

In Oxfordshire, Oxford tops the chart for infestations of Japanese knotweed with 21 occurrences recorded.

Littlemore, specifically, has 17 cases of the plant while Henley has 12, Woodstock 6 and Wallingford 4.

Witney Gazette: Picture: Environet UKPicture: Environet UK

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 metres tall
  • In August the plant blooms, with small clusters of creamy white flowers appearing on the upper leaf axials.

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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 neighbour’s property, there’s no reason to panic.

“By publishing the 2022 hotspots for Oxfordshire 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.”


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