West Dorset hotspots of invasive Japanese knotweed revealed

Japanese knotweed is a rapidly growing plant responsible for damaging homes, pavements and drains. It can spread up to seven metres horizontally.

As Japanese knotweed’s summer growth period draws to a close, invasive plant specialist Environet has analysed the latest data from its live online tracker to reveal this year’s Japanese knotweed hotspots.

Infestations: 

• Dorchester - 95
• Bridport - 61
• Weymouth - 39
• Lyme Regis - 30
• Beaminster - 15

With a total of 406 known infestations across Dorset, there is one occurrence of Japanese knotweed in every 10km².

Japanese knotweed usually emerges in March or April and grows rapidly to reach up to 2.5 metres in height by mid-summer. It is identifiable by its hard, bamboo-like canes and distinctive shield-shaped bright green leaves which grow in a zigzag pattern along the stem.

Mature plants flower in August, becoming covered in clusters of delicate tasselled creamy-white flowers. Knotweed does not produce viable seeds as all the plants in the UK are female, so it is usually spread accidentally through the movement of soil or gardening waste, or via rivers and streams when pieces of rhizome break off and take hold in new locations. 

Tackling knotweed costs the UK economy nearly £250 million a year and homeowners are one of the groups most at risk – not only from potential damage to their property, outbuildings and gardens, which can be costly to repair, but also from legal risks arising from encroachment or when properties are sold. 

It is unlawful to cause it to grow in the wild or to allow knotweed from your own property to invade neighbouring land.

Nic Seal, founder of Environet, said: “Vigilance is the best way to protect your property from the risks posed by Japanese knotweed. Make sure you know what knotweed looks like and how it differs from other common garden weeds like ivy and bindweed, so you can keep an eye out for it in your garden and neighbourhood.

"Knotweed is easily identifiable during summer, but as we head through the autumn and into winter, the above-ground growth dies back and it becomes much harder to spot. It’s also easier to conceal, so anyone viewing a property to buy should be extra careful.

“There are lots of horror stories out there but with professional help, knotweed can be successfully treated and a property’s value can be largely restored.”

According to Environet UK, around 4 to 5% of the UK’s houses are currently affected, whether directly or indirectly.