Japanese Knotweed

Latest news

9 March 2010 - News release: Bug tackles UK’s knotty problem.

On this page

Why is Japanese knotweed a problem?

Image of Japanese KnotweedJapanese knotweed is native to Japan, Taiwan and China, and was introduced to Europe as an ornamental plant in the early 19th century. It is a large vigorous weed that appears to have no natural enemies in Britain. It can colonise most habitats and is regarded as a troublesome pest in many parts of the country because of its rapid invasion and domination of habitats, which results in the exclusion of other plants. It can damage property (for example by growing through tarmac or even the floors of houses) and therefore needs to be cleared from development sites. The species also causes problems in terms of flood management. It increases the risk of riverbank erosion when the dense growth of the plant dies back in the autumn exposing bare soil. It can also create a flooding hazard if the dead stems are washed into the streams and clog up the channel. A fragment of root as small as 0.8 grams can grow to form a new plant.

The New Atlas of the British and Irish Flora (published in September 2002) found that the species has increased its range considerably since the previous Atlas published in 1962.

Government Action

The Government is aware of the problems of invasive non-native plants such as Japanese knotweed. While there is no statutory requirement for landowners to remove the plant from their property, because of its potential harm to native species, it is listed on Schedule 9 and subject to section 14 of the Act 1981, which makes it an offence to plant, or cause this species to grow, in the wild. Both the Police and local authorities have enforcement functions for the 1981 Act. In addition, Japanese knotweed is regarded as controlled waste and has to be disposed of at licensed sites or by burning on site.

The cost of a national eradication programme using current techniques is prohibitively expensive, estimated in the Defra Review of Non-native Species Policy to be in the region of £1.56 billion. However, the Environment Agency does take local measures if flood defences are compromised (using risk assessment and local knowledge). In Cornwall, a more proactive programme has been implemented by the Agency in association with the Cornwall Knotweed Forum.

Defra has contributed funding to scientific research into the natural control of Japanese knotweed, commissioned in collaboration with Cornwall Council, the Environment Agency, the Welsh Assembly Government and others. This study has been undertaking the necessary research to establish whether natural control is a feasible method for the long-term, sustainable management of Japanese knotweed in Great Britain. The project has identified a potential control agent, an insect which is highly specific to Japanese knotweed. The research is currently undergoing rigorous scientific and regulatory examination, and consideration of any risks, which will form the basis of a decision on whether any release of the control agent can go ahead.

The Environment Agency (in partnership with Defra and Network Rail) has published the knotweed code of practice for those involved in the development industry, which faces the problem on a large scale.  Much of the advice also holds good for householders and private landowners. Page 6 sets out the relevant legislation under the Act 1981 and "controlled waste" issues in more detail. The code also gives practical advice on the use of herbicides and other control methods.


  • Japanese knotweed is an invasive non-native species which, having been brought to Britain as an ornamental garden plant in the mid-nineteenth century, is now established in the wild.
  • It is an offence under section 14(2) of the Act 1981 to "plant or otherwise cause to grow in the wild" any plant listed in Schedule 9, Part II to the Act.  This includes Japanese knotweed. 
  • It is not an offence to simply have it growing in your garden or on your land and there is no legal requirement to control it if it is (unless doing so forms part of a legally binding contract or agreement with another party).
  • It is not listed in the Weeds Act and is not a 'notifiable' weed so there is no need to report its presence on your land (unless doing so forms part of a legally binding contract or agreement with another party).
  • Any Japanese knotweed contaminated soil or plant material that you intend to dispose of is likely to be classified as 'controlled waste' under the Environmental Protection Act 1990.  Untreated knotweed is not regarded as a 'hazardous waste' under the Hazardous Waste Regulations 2005 but material containing knotweed that has been treated with certain herbicides could be.
  • The Control of Pesticides Regulations 1986 require any person who uses a pesticide to take all reasonable precautions to protect the health of human beings, creatures and plants, safeguard the environment and in particular avoid the pollution of water.  Approval from the Environment Agency should be sought before application of pesticides in or near water.
  • Vigorous growth can damage buildings and hard surfaces as well as causing problems for native wildlife.  Whilst it is therefore prudent to control and dispose of Japanese knotweed it should be done in such a way that does not contravene the above legislation.

Further information

Enquiries regarding invasive non-native weeds such as Japanese knotweed, or injurious weeds such as Common ragwort, are dealt with by Natural England’s Incentive Schemes Services Section.

For enquirers based in

  • southern England call - 0118 9392256,
  • for the eastern counties call - 01223 533588,
  • for counties in the Midlands call - 01905 362833 and
  • for counties in northern England call - 01132 303705.

You may also find the Environment Agency’s short factsheet on Japanese knotweed useful.

Cornwall County Council is particularly proactive in tackling the significant knotweed problem in that region.  Its Japanese Knotweed pages offer advice relevant to householders and landowners anywhere in Great Britain.

Page last modified: 29 March 2010
Page published: 23 October 2008

You may also be
interested in...