Gardeners could be breaking the law by dumping destructive Japanese knotweed illegally because councils are providing misleading information on tackling the menace, a study has found.
The fast-growing weed, which can grow through brickwork and concrete, is estimated to cost £165 million a year to control in the UK.
It has a root system that can extend up to three metres in depth and seven metres in all directions and grow into building foundations and drains, causing serious structural damage.
Mortgage lenders can refuse loans for homes blighted by the problem. But poor advice on websites and provided by some councils could be causing needless worry and expense, according to scientists from the University of Exeter.
The researchers found knotweed guidance on websites run by NGOs, weed-control firms and local government varied wildly, and was sometimes “contradictory and potentially misleading”.
While some councils, such as Devon and Cornwall, provided valuable and accurate information, others had issued conflicting online advice that could lead to “potentially unlawful” decisions, they said.
Dr Beth Robinson, from the University of Exeter’s Environment and Sustainability Institute, said: “This does raise concern that if those responsible for domestic gardens consult only the website of their local government authority, the quality and clarity of the information received could vary geographically.
“It is important to provide clear advice about waste disposal of Japanese knotweed, as it can regrow from small fragments of rhizome and incorrect disposal of waste material can result in further spread of this plant.
“We recommend that local and national authorities collaborate and work towards disseminating more consistent messages.”
The fast-growing weed needs to be sprayed with herbicides for up to three years while the plant or any soil containing it must be disposed of by a licensed waste carrier at a licensed waste site.
Gardeners can face criminal prosecution and be fined up to £2,500 for not controlling the plant. Organisations can be fined up to £20,000.
Rob Higgins, director of Taylor Total Weed control, a company that tackles Japanese knotweed across Wales and the West Country said: “There’s not enough information out there. We get a lot of people saying ‘I keep pulling it out and putting it in my green garden waste bag’. That will go to the council and could be made into compost that will spread the problem to other people. They get paranoid when they have knotweed. You get people crying on the phone because they can’t sell or buy a house.”
The plant should be dealt with on a case-by-case basis, according to the scientists from the University of Exeter, writing in the journal Applied Ecology. While professionals may sometimes have to be called in, small-scale appearances of Japanese knotweed in domestic gardens may not require expert treatment, they added.