Japanese knotweed hotspots in the UK revealed

A study has revealed the hotspots in Britain for the nations’s most invasive plant Japanese knotweed which can result in house sales falling through as it deters buyers.

Bolton in Lancashire is the worst affected areas overall, with 652 infestations within a four kilometer radius, followed by Bristol in the South West and Capel Garmon in Conwy, North Wales.

The survey from removal specialists Environet UK also found that Clapham Common is the worst affected area in London.

Described by the Environment Agency as ‘indisputably the UK’s most aggressive, destructive and invasive plant’, Japanese knotweed grows rampantly along railways, waterways, in parks and gardens and is notoriously difficult to treat without professional help.

Environet has analysed data from its online heat map launched earlier this year, which records Japanese knotweed sightings across the UK. The map is intended to inform local home owners and potential home buyers of the local presence of Japanese knotweed, enabling them to enter a postcode to discover the number of reported knotweed sightings nearby, with hotspots clearly visible in yellow or red.

Other hotspots include Rotherham, Nottingham, Madeley in Shropshire, Shanklin on the Isle of Wight, Norwich and Newcastle.

Japanese knotweed can deter buyers, making a property difficult to sell and prevent a mortgage lender approving a loan unless a treatment plan is in place with an insurance backed guarantee, thereby impacting a property’s value by around 10%.

Sellers are required by law to inform potential purchasers whether their home is, or has been, affected by Japanese knotweed, which can act as a deterrent even if the infestation has been treated.

Environet estimates that Japanese knotweed currently affects 4 to 5% of UK properties, wiping a total of £20 billion off house prices.

‘Japanese knotweed has become a major problem across the UK, with areas of industrial heritage such as Bolton and North Wales particularly badly affected. One theory is that land moved during mining and heavy industry helped knotweed to spread, while the practice of dumping ballast from ships in the nineteenth century could have allowed it to take hold in port cities such as Bristol,’ said Nic Seal, managing director of Environet.

‘Anyone thinking about buying a property in or around these hotspots would be wise to check the number of infestations in the proximity of their postcode and consider instructing a specialist to carry out a Japanese knotweed survey on the property to check for evidence of the plant,’ he explained.

Japanese knotweed arrived in the UK in the 1840s, in box of 40 Chinese and Japanese plant species delivered to Kew Gardens. The plant grows at the incredible rate of around 10 centimeters a day from May until July and when it is fully grown it can stand up to three meters tall.

Knotweed blooms in late summer, when it becomes covered in tiny creamy white flowers. It can lie dormant under the ground for up to 20 years before suddenly re-growing.