Japanese knotweed fact file

  • Japanese Knotweed and agriculture – under cross compliance Japanese knotweed should be controlled.
  • Its scientific name is Fallopia Japonica but the family also includes derivatives such as Giant Knotweed and Himalayan Knotweed.
  • Japanese knotweed is native to Japan, Taiwan and China
  • It was introduced to Britain by the Victorians in the 1800s as an ornamental garden plant.
  • It grows rigorously and spreads rapidly – up to 2m in one season. Its underground root systems can stretch for 7m.

    Knotweed against a garden fence

    Problems with neighbours

  • In the UK, it’s illegal to plant, or cause this species to grow, in the wild but it’s not an offence to simply have it growing in your garden or on your land.
  • However, if it escapes, or you cause it to spread to a neighbouring house or garden, you may be liable with litigation against you.
  • Treated as controlled waste, it cannot be dumped in domestic green recycling bins. Only licensed landfill sites can take it – and with prior notice and waste transfer documentation is needed.
  • It can grow through floors of houses, cracks in asphalt, concrete and walls and into drains and cause significant damage

    Knotweed next to underground pipe and rubble

    Drainage system damage

  • In Japan, the plant is used in traditional medicine and is known as “itadori” which means as ‘take away pain’.
  • Other common names include: donkey rhubarb, gypsy rhubarb, Hancock’s curse, Mexican bamboo, German sausage plant and Japanese bamboo.
  • Japanese knotweed treatment costs the British economy millions of pounds each year to manage. And it’s estimated that the cost of controlling it could add 10 per cent-plus to a development project.
  • A DEFRA working group estimated that it would cost £1.5 billion to control it across the UK.
  • Japanese Knotweed is still spreading in the UK. According to the Japanese Knotweed Alliance, only the Orkney Isles are exempt.
  • London’s 2012 Olympics organisers spent four years controlling the weed .
  • In Japan, natural enemies keep it under control.
  • Since 2000, scientists at CABI – the Centre for Agricultural Bioscience International – has been working to stop the spread of Japanese knotweed in a major research project, which has cost about £600,000 over five years.
  • A plan to introduce plant-eating predators and knotweed disease from Japan is currently being allowed by the government. It has been the first time that biocontrol – the use of a natural enemy to control another pest – has been used in Europe to fight a weed. It’s estimated that it could take between 5-10 years from release to bring under effective control.

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