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Japanese Knotweed

Fighting Back Against Japanese Knotweed with Geomembranes

Weed barrier

Known today as one of the biggest horticultural menaces in the UK, Japanese Knotweed was once imported from Japan by the Royal Botanic Gardens at Kew as an exciting new addition to the collection and was a welcome exotic plant in many Victorian gardens. Today the weed is rampant across the UK and the race is on to find a way to control this pest, which causes millions of pounds worth of damage to buildings and infrastructure every year.

Ironically, Japanese Knotweed was purposefully planted in some areas as a way to stabilise lose soil but the weed soon spreads to uncontrollable levels and can survive in a wide range of conditions. It’s considered a danger today that failing to control the plant can result in prosecution and hefty fines.

Japanese Knotweed is such a problem because it has no natural predators in the UK, whereas in its native Japan volcanic ash in the atmosphere and certain insects keep it well under control. The plant is of a particular problem to the construction industry as it’s so prolific and is very expensive to remove or destroy.

It cost more than £70m to clear just 10 acres of the plant from the London Olympics site during the construction phase. It can penetrate tarmac and concrete, causing extensive damage to roads, pipes, paving, foundations and pretty much anything which gets in its way. Removing it is no easy option as the weed’s roots can grow over 2m deep and even the smallest piece of root left in the ground can spawn a new plant. Pesticides can control the weed but there are concerns about the damage these can do to native plants and animals.

Whilst the control of Japanese Knotweed can never be fully guaranteed, another option to consider is the use of specialist geotechnical products. Heavy duty root and weed barriers are specifically designed to suppress the growth of Japanese Knotweed and can be one of the most cost-effective and straightforward options for attempting to control the weed. Tough and durable root and weed barriers can help protect structures which are commonly threatened by Japanese Knotweed such as roadways, pipelines and housing by preventing the plant from penetrating the ground surface.

Standard geomembranes may not be effective against Japanese Knotweed as the plant will easily break through any holes or joints in the membrane. In some cases, as well as laying the root barrier horizontally, it will also need to be laid vertically in a continuous sheet to prevent the horizontal growth of Japanese Knotweed by completely containing the roots of the plant.

Japanese Knotweed costs the UK economy £166 million per year in treatment costs in home and land devaluations but geotechnical solutions from SIG Construction Accessories could save you time and money on eradicating the weed from your next project. For advice on the best solution for your project please contact our Geotechnical Centre on 0844 449 0050.