Advice for landowners and gardeners

As a landowner, gardener, riparian owner or wildlife site manager it is important to be aware of Japanese Knotweed and, if you have it on your site, to control it.

Japanese knotweed next to a footpath Japanese Knotweed on a river bank Japanese Knotweed on a derelict site

Advice for Landowners

Japanese Knotweed is one of Britain’s most invasive plants and the prevention of its spread is a legal obligation for landowners under the Wildlife and Countryside Act 1981. It is difficult and expensive to manage but non-intervention is not really an option. Early treatment of a new colony is quicker, cheaper and preferable to leaving it to become established.

If you have Japanese Knotweed on your site(s) it important that you devise a strategy to treat and control it. When devising an action plan for Knotweed treatment you should consider the following:

ObjectiveProposed action to achieve objective
Determine priority sites for treatment of knotweedUse the following criteria to identify sites and prepare a programme of treatment.

Suggested criteria:

Areas of nature conservation value
Areas identified for landscape improvement work
Areas of amenity interest
Areas which are causing rapid spread of Knotweed onto new sites e.g. stream and river banks
Areas where funding opportunities can be used to include Knotweed treatment
Sites where Knotweed is causing a problem for others e.g. damage to property, spreading into private gardens etc.
Areas where the presence of Knotweed is a visual eyesore
Sites where resources are available for long-term maintenance
Sites where Knotweed is creating a safety hazard
Sites which are the subject of significant complaints from the public
Seek funding to assist in a programme of Knotweed controlWhere appropriate, land holding committees should be asked to consider allocating an annual budget for treatment of Knotweed on their land.

Where appropriate, provision for control of Knotweed should be included in estimates for major landscaping and engineering schemes.

Explore sources of funding e.g. grant aid, industrial sponsorship.
Develop a strategy for responsible treatment of knotweedIdentify sites with Japanese Knotweed.

Prepare a control programme for each site.

Ensure relevant specifications are used in contract documents for building, engineering, landscaping etc. to prevent spread.

Ensure an appropriate control/eradication method is used for each site.
Carry out treatment of Knotweed on sites already managed by your organisationEstablish whose responsibility it is to supervise and implement treatment of Knotweed.

Ensure staff/contractors hold a Certificate of Competence to use herbicides.
Develop the direct provision of manpower for the treatment of KnotweedEstablish a good skills base within the staff or establish working relationships with reputable contractors.
Develop monitoring schemes to record effectiveness of Knotweed control programmesMonitor all sites where Knotweed control is carried out on your site(s)

Transfer data to Devon Biodiversity Records Centre.

Share experiences with the Devon Knotweed Forum and other Agencies.
Develop a strategy for the treatment or disposal of soil contaminated with Knotweed and cut Knotweed stems or crowns.Establish an area for the controlled disposal of Knotweed contaminated soil which could then be treated over a 3 year period.

Establish an area for the controlled dumping of cut Knotweed stems for composting or drying for burning. This could be an area already contaminated with Knotweed. Regular checks should be made to ensure there is no re-growth and appropriate treatment should be used.
Ensure all relevant staff are aware of the problems of Japanese Knotweed and what the strategy is for controlling it on site(s)Staff awareness training to include identification, relevant legislation, preventing spread, who to notify if Knotweed is found, Knotweed control, who is responsible for what.

Advice for Riparian owners

Japanese Knotweed thrives on riverbanks and can easily spread downstream if the bank erodes and fragments of rhizome, crown or stem break away. Treatment options are more limited because of the need to prevent pollution of watercourses. You will need to consult the Environment Agency before using herbicide. Telephone the Ecological Appraisal Team for Devon on 0370 850 6506, or email You can also use the plant tracker website to report all invasive plants to the Environment Agency to help them map and monitor the spread of these species.

Japanese Knotweed also causes other problems for riparian owners including:

  • Dense stands impede access for anglers and walkers along river banks.
  • Riverbank inspection is made more difficult in summer.
  • River bank maintenance costs are greatly increased.
  • Maintenance can lead to further spread by allowing distribution of plant fragments.
  • Rapidly growing rhizomes and shoots can affect the integrity of flood defence structures.
  • Damage to flood prevention structures is expensive to repair and is on-going unless the plant is controlled.
  • Bare soil exposed in the winter can cause increased soil erosion, especially on steep river banks.
  • Decaying plant material in the winter can be washed down river and create blockage and risk of flooding.
  • Dense stands on bank sides can impede flow in times of flooding thus exacerbating flooding.

As a riparian owner your non-chemical treatment options are cutting, pulling or grazing. Although these are labour intensive, long-term options they are preferable. However, extra care should be taken to prevent Knotweed fragments entering the river and causing spread downstream. Avoid using machinery that cuts up and scatters plant fragments.

If these mechanical treatments are impracticable due to factors such as terrain then chemical control is your next option.

For operations involving chemical treatment in or near watercourses you are required to obtain the written approval from the Environment Agency.

The Environment Agency can assess whether there is any risk to drinking water supplies, water for spray irrigation, or wildlife. The European Commission sets stringent standards for the amount of herbicides and pesticides allowed in drinking water and the Environment Agency is responsible for making sure the risk of contamination is minimized.

Ensure staff or contractors have a Certificate of Competence to use herbicides in or near water (Environment Agency can advise).

See Control of Knotweed / Chemical Treatment.

Remember: any work carried out near water is potentially dangerous.

For further advice see:

Advice for Gardeners

Japanese Knotweed is an attractive plant and was originally brought into the UK in 1825 by the Victorians. Gardeners soon discovered how difficult it was to keep under control and by 1886 the plant had escaped from gardens and had become naturalized throughout the UK.

Where rhizomes or stems were composted or left on road verges or waste ground the plant started to establish and spread.

If you suspect you have Japanese Knotweed on your property you should take care not to allow it to spread. Even the smallest piece of rhizome, stem or crown can potentially form a new plant. Compost Japanese Knotweed separately, preferably on strong plastic sheeting so it is not in contact with the ground. Check the compost regularly to ensure it is not sprouting. Ensure that it is fully decomposed before spreading it on the garden. Do not shred or strim the plant as this could cause rapid spread. Mowing is only advised if you have a collecting box for mowings which can then be composted. Do not dig Japanese Knotweed as this is known to increase stem density and it encourages sprouting and spread.

Hand pulling or cutting the plant is a good method of control but will take several years for the rhizome to be exhausted and die. Leave the material on a plastic sheet to dry and then burn it. Do this on site to prevent spread. The cutting and pulling of stems encourages the plant to send up more shoots which can in turn be pulled.

You can also use chemical herbicides, glyphosate is recommended but treatment will need to be ongoing and may take several years depending on how established the colony is.

Avoid digging within 7 meters of a colony of Japanese Knotweed, and avoid moving the soil around the garden as the soil could contain rhizome.

Do not take Japanese Knotweed material to your local recycling centre, Japanese Knotweed has to be treated as ‘controlled waste’. Do not remove Japanese Knotweed material from the site unless you have made a prior arrangement with a licensed landfill site for deep burial. Treatment on site is the preferred option.

Advice for Wildlife Site Managers

Japanese Knotweed is a highly invasive alien plant species which, if allowed to establish, will out-compete native flora and reduce the wildlife value of a site. Early treatment of a colony is advisable before it becomes established as large stands are particularly difficult to eradicate. You also have a legal obligation to prevent its spread under the Wildlife and Countryside Act 1981.

If Japanese Knotweed is found on a wildlife site it is important to plan and commence a control programme as soon as possible. The treatment of this plant can be long-term and expensive but ignoring it is not an option as it is highly invasive. It will continue to spread if left alone. Japanese Knotweed is also capable of sprouting from cut rhizome or stem so the safe disposal of the plant material is vital to prevent spread.

See Preventing Spread

The choice of treatment is limited on wildlife sites as your objective is to help prevent damage to the site, loss of native flora and loss of wildlife value. The use of herbicides is always an option and there are specific brands of systemic herbicides that can be wiped onto the plant’s leaves to specifically target only the plants you want to eradicate.

If your site is near a watercourse you will need to consult the Environment Agency before using herbicide. Telephone the Ecological Appraisal Team for Devon on 08708 506 506.

See Advice for Riparian Owners (above)

There are two main non-herbicide treatment options to consider:


As a method of control is only really useful when treating small or new infestations where only a few stems have established. It is an excellent method to use on sites with native or sensitive species growing and where the use of herbicides is undesirable as it specifically targets Knotweed plants. Care should, however, be taken to avoid trampling valuable flora in the vicinity.

Stems should be pulled regularly when they reach full height. They should be pulled near the base to include some rhizome. Control of a small infestation could be achieved in 3 years but this method requires regular, sustained treatment to work. This is labour-intensive but an ideal activity for volunteer work days.

You must ensure that pulled stems are disposed of correctly to avoid spread.


Japanese Knotweed is used as animal fodder in the Far East and here in Britain it is known that cattle, sheep, horses, donkeys and goats graze the plant. Animals prefer the young shoots as they emerge in the spring and after about June the stems become rather woody. Grazing may reduce shoot densities and height but will not eradicate it. Although grazing can help reduce the spread into uninfested areas it is not a method of control. Dead stems should be cut back in winter as these can deter grazing in the spring. Continued grazing will ensure the supply of new shoots throughout the growing season.

Grazing is therefore not an eradication tool but is helpful in suppressing the plant and reducing spread.

Herbicide treatment

For operations involving chemical treatment in or near watercourses you are required to obtain the written approval from the Environment Agency.

This is not an easy option and the use of herbicides is still a labour-intensive and expensive operation. Dense stands of Japanese Knotweed can be treated with a glyphosate-based herbicide, such as ‘Roundup Pro Biactive’. If the Japanese Knotweed is sparsely distributed, use 2,4-D amine, which is specific to broadleaved plants and will not harm the grasses. It may take two or three years to fully control the plant. More effective control can be achieved if Japanese Knotweed is cut and sprayed in early summer, then sprayed again in late summer, just before the winter dieback.

More targeted methods of applying herbicides are being developed for sites where it is important to protect the native flora, this includes using a weed wiper or herbicide glove to apply the herbicide directly to the leaves of the plant, or direct injection, rather than spraying.

The plants should be treated between March and October when they are in the growing phase, the late summer is the best time. Plants can take up to 6 weeks to show signs of die-back.

For more information on chemical treatment see Control of Knotweed / Chemical Treatment

Further reading:

‘Guidance for the control of invasive plants near watercourses’, available from the Environment Agency

Child, L.E. and Wade, P.M., The Japanese Knotweed Manual , Packard Publishing Limited, Chichester , 2000, 123 pp, ISBN 1085341-127-2.

For further information see:

How can you help?

Without surveying and recording the distribution of Japanese Knotweed there is no way of knowing where it occurs, whether it is increasing and the typical habitats it colonises. Knowing the full extent of the problem of Japanese Knotweed colonisation in the county will help the Devon Knotweed Forum identify priorities for control and management. It is therefore important to report any sightings of the plant in the county to the Devon Biodiversity Records Centre. If you have a colony of Japanese knotweed please inform the Devon Biodiversity Records Centre to keep us up to date by filling in their form. Please note the Devon Biodiversity Records Centre is not responsible for controlling Japanese Knotweed.