Japanese knotweed: Top 10 hotspots where the invasive weed is most active in the UK

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Japanese knotweed can be expensive and tough to remove, especially when it is left untreated for a significant amount of time. This dangerous plant will grow in the cracks of concrete, brickwork and patios – but where in the UK is it most active? As the plant reaches its peak growing season, the experts at Environet have revealed the top spots across the country experiencing an infestation of Japanese knotweed. Is your area affected?

There is no easy way to get rid of Japanese knotweed growing on your property, but it could cause significant issues for both you and your neighbours if left untreated.

As knotweed reaches the height of its growing season, established plants will begin to expand, making it easier to identify in your local area.

To help you spot the signs of this concerning weed, invasive plant specialist, Environet UK, has shared the top 10 hotspots for 2022.

So where in the country will you find the worst infestation?

Japanese knotweed hotspots in the UK

Environet UK has analysed data from its online Japanese knotweed heat map, populated with 55,000 known infestations across the country.

The map enables homeowners to understand the risk knotweed poses to their existing home, or a future property they wish to buy.

According to the latest data gathered by Environet, Bolton, Greater Manchester, is the most affected region in Great Britain – taking the top spot for yet another year.

The top-ranking hotspot has recorded 684 infestations within a 4km radius, making it the worst affected area so far this year.

According to Environet data, the top top 10 spots are:

  1. Bolton, Greater Manchester – 684 infestations within a 4km radius
  2. Bristol – 475 infestations within 4km radius
  3. St Helens, Merseyside – 441 infestations within 4km radius
  4. Blackburn, Lancashire – 407 infestations within 4km radius
  5. Capel Garmon, Snowdonia, Wales – 398 infestations within 4km radius
  6. Llanelli, South Wales – 389 infestations within 4km radius
  7. Cardiff, Wales – 361 infestations within 4km radius
  8. Rotherham, Yorkshire – 306 infestations within 4km radius
  9. Streatham, South West London – 300 infestations within 4km radius
  10. Nottingham – 225 infestations within 4km radius 
  11. Sheffield – 225 infestations within 4km radius

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How can Japanese knotweed affect buildings?

According to Environet’s research, approximately five percent of homes are currently affected by knotweed, either directly or indirectly.

The roots can grow as deep as three metres and spread up to seven metres wide, making it hard to control without professional help.

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.

“Anyone living near or moving to one of these hotspots would be wise to check their garden carefully, enter their postcode into the Exposed heatmap to find out how many known occurrences are nearby and if in doubt, seek expert help.”

How to spot Japanese knotweed

Knotweed hibernates over winter but in March or April, it begins to grow, with red or purple spear-like shoots emerging from the ground.

These unmissable shoots will quickly grow into lush green shrubs with pink-flecked stems and bamboo-like canes.

The plant has the potential to grow as deep as three metres and spread up to seven metres wide.

By mid-summer, the plant grows at a rate of around 10cm per day, with mature plants forming dense stands and small cloisters of creamy white flowers by August.

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