Disposing of Japanese knotweed

Japanese knotweed waste is likely to be controlled waste. In England and Wales it must either go to a landfill or incineration site with the right permit, carried by a registered waste carrier, or be dealt with under strict conditions on the site where it grew. Because a new plant can grow from rhizome pieces as small as 1 cm, most homeowners should ask a specialist to handle disposal as part of a treatment plan.

The rules below are for England, with the differences in Wales at the end. Scotland and Northern Ireland have their own rules, which are not covered here.

Controlled waste

Japanese knotweed is not named in the Environmental Protection Act 1990, but GOV.UK guidance says soil or plant material contaminated with it may be classified as controlled waste. RICS goes further, stating that contaminated material a person discards is likely to be controlled waste and that sections 33 and 34 of the Act are the most relevant.

Under the duty of care in section 34, anyone who produces, carries, keeps, treats or disposes of controlled waste must take reasonable measures to stop it escaping, transfer it only to an authorised person and pass on a written description of it. Householders in England and Wales must take reasonable steps to make sure their household waste goes only to an authorised person, and breaching the duty of care is a criminal offence. In practice, you are responsible for checking who takes your knotweed away.

Taking knotweed off site

If knotweed cannot be dealt with on site, the GOV.UK guidance for England requires it to go to a landfill or incineration facility with the correct permit, and you must first check that the permit covers invasive plant material. The waste must be carried by a registered waste carrier, and you must tell the Environment Agency where it was sent. Loads must be covered and vehicles cleaned afterwards, and knotweed soil must not be mixed with other surplus soil or sold as topsoil.

The guidance also rules out exemptions: "You cannot get a waste licensing exemption for the use of Japanese knotweed."

Waste charges add up quickly. RICS notes that even a small infestation can cost several thousand pounds in waste charges alone, before any other removal costs.

Burial on site

In England, knotweed may be buried on the site where it grew, under the GOV.UK guidance and the Environment Agency's regulatory position statement RPS 178. The minimum depth is 5 metres, or 2 metres if the waste is sealed in a geotextile membrane, which must be undamaged, large enough to keep joins to a minimum, securely sealed, UV resistant and able to last at least 50 years.

The two England sources disagree on notice: GOV.UK says to notify the Environment Agency at least one month before burial, RPS 178 at least one week. Giving at least one month's notice is the safer course.

RICS says on-site burial or stockpiling may reduce waste costs on large sites, but is unlikely to suit standard residential properties.

RPS 178 conditions

RPS 178 sets out when the Environment Agency will not normally enforce the permit requirement for on-site treatment or burial in England. The conditions are:

• a management plan
• burial on land of low habitat value, in an area unlikely to be disturbed, more than 7 metres from an adjacent landowner's site
• no groundwater pollutants
• storage for no more than 12 months, or 6 months if a D7 exemption is registered
• records kept for 2 years

The position statement does not remove the legal need for a permit where one applies, and it is due for review by 12 August 2028. Its 7 metre distance is a burial condition only, unrelated to the old 7 metre rule in the 2012 RICS paper, which RICS replaced in 2022.

Screened or sieved knotweed soil may be reused only on the original site, in a restricted area. Under RPS 178 it must not be used within 50 metres of watercourses or protected areas, on boundaries with neighbours, on lawns, gardens or amenity areas, or in places used by people or livestock.

Burning

Under the GOV.UK guidance for England, a business planning to burn knotweed must tell the Environment Agency at least a week beforehand, tell the council's environmental health officer, register a D7 exemption and follow local byelaws. An individual need only check with the council that burning is allowed. Crowns and rhizomes may survive burning, so the burial or disposal rules still apply to whatever is left.

Composting dead canes

In both England and Wales, dead, brown knotweed canes can be composted on site, provided they are cut, not pulled, at least 10 cm above the crown. The rule covers only dead canes cut in this way.

Herbicide treatment

In England, only approved herbicides may be used, by someone who holds a certificate of competence or works under the direct supervision of someone who does, and a COSHH assessment may be needed. Protected sites such as SSSIs need Natural England's permission, and treatment near water needs the Environment Agency's agreement, which you apply for online or by form.

GOV.UK says treatment usually takes at least 3 years, and advises against treating knotweed yourself unless you have the right skills and experience. RICS uses a different measure for treatment programmes: at least four years of treatment and monitoring before a completion certificate.

Wales

In Wales, Natural Resources Wales Regulatory Statement 058.3 mirrors the England rules, with some differences:

Using a specialist

A specialist can set out the right approach for your site in a knotweed management plan, which is one of the RPS 178 conditions for on-site treatment or burial. If the waste has to leave your property, ask them to confirm the registered carrier and the permitted site it will go to.