Japanese knotweed

What to do if you have Japanese Knotweed

Japanese knotweed (which has the botanical name Fallopia japonica) is a plant that is extremely invasive. As the name suggests, it is not native to the UK but has come from Japan.

Serious structural damage has been recorded to buildings, hard-standing, walls and drains where Japanese knotweed is found.

Japanese knotweed is so damaging that many mortgage lenders will not give you a mortgage if you have it on or near the property you are hoping to buy.

Where lenders will provide you with a mortgage they will require you to implement a significant management and removal plan which could include chemical treatment or excavation to completely remove all traces of the plant. Either way, this may well prove a lengthy and costly undertaking.

If you’re not sure what Japanese knotweed looks like here is a helpful factsheet that will help you to identify it.

Because it is such a recognised risk to property, Japanese knotweed is governed by legislation.

  • Under the terms of the revised Anti-Social Behaviour, Crime and Policing Act 2014, you could be issued with a community protection notice to force you to control non-native invasive plants on your property. You could face a fine of up to £2,500 if an unreasonable lack of action to control or remove the knotweed has a detrimental effect on the quality of life of those nearby.
  • The Wildlife and Countryside Act 1981 makes it an offence to cause Japanese knotweed to grow in the wild. It is also an offence to knowingly allow knotweed to spread from your property.
  • Under the Environmental Protection Act 1990 and Duty of Care Regulations 1991, Japanese knotweed material and material contaminated with Japanese knotweed must be removed to a licensed landfill site for disposal, accompanied by appropriate waste transfer documentation.


The Royal Institute of Chartered Surveyors (RICS) has an information sheet which you can download here.

RICS has also partnered with the Property Care Association to establish the PCA Invasive Weeds Control Group trade group for Japanese knotweed specialists. It is a list of reputable consultants and removal contractors whom you can turn to for help with your knotweed problem.

  • Where a known or suspected presence of knotweed is highlighted a specialist knotweed survey should be carried out to establish the risk and provide advice on a remediation solution.
  • Most UK mortgage lenders will want to see evidence of a commitment by the owner of the property to fund, in advance, a long-term chemical treatment programme against Japanese knotweed, or provide instant eradication by way of excavation and removal. Chemical treatment can take approximately two to three years to provide effective control of the knotweed.
  • Even after chemical treatment, the rhizome (root) of Japanese knotweed can remain dormant for many years. Excavation and removal of knotweed is often preferred. If you can negotiate an instant removal of knotweed by excavation, do so.
  • A guarantee is often required on any remedial works, with durations of between five and ten years being the norm. A guarantee should ensure that if there is any recurrence of knotweed growth (because of a defect in the remedial works undertaken) it will be treated and controlled at no additional expense to the property owner.
  • Because treatment programmes can stretch over many years, mortgage lenders will often look for an insurance backed guarantee (IBG) product, such as that provided by PCA IWCG members. This ensures that if a knotweed contractor providing a guarantee goes out of business before the end of the cover period, the customer will be protected by either another PCA registered company stepping in to take on the liability, or a refund of the monetary sum left on the contract.
  • On development sites, Japanese knotweed needs to be managed and handled responsibly. Any works conducted to control or eradicate the plant should be completed according to the Environment Agency and PCA codes of practice for the management of Japanese knotweed.