Japanese Knotweed (Fallopia Japonica) was first brought to the UK by the Victorians as an ornamental plant but now costs £150 million a year to control. It has no value except as an ornamental plant and has no known predators. Incredibly invasive, it can grow four inches a day from April to October and a tiny root can establish itself as a plant in just ten days. Apparently, solid structures such as tarmac and flooring in houses are no barrier to its growth and the weed also creates a risk of flooding if its leaves clog waterways.
Knotweed is recognised by its shovel‐shaped leaves, bamboo‐like stem and white flowers produced in autumn. If you discover the plant on your property, these are some of the steps you should take to prevent further problems:
- Immediately create a 21ft exclusion zone around the suspect plant.
- Do an initial spray with a Glyphosphate‐based weed killer.
- Do not excavate or move soil from the exclusion zone without instruction from the local authority.
- Cutting should be done with sharp secateurs or pull it out by hand to avoid dispersal of fragments.
- Wash feet and clean shoes when leaving the contaminated area.
- If you cut down knotweed, you can burn it on site or bury it ‐ 16ft deep, covered with a root-barrier membrane and with inert topsoil ‐ with permission from the Environment Agency. Material taken from the site must be disposed of at a licensed facility.
The Environment Agency describes Japanese Knotweed as the most invasive species of plant in Britain and is notably the UK’s most aggressive, destructive plant. Landowners are under a statutory duty to be proactive in the control and eradication of it. All parts of the plant and any soil contaminated with it are classified as controlled waste and must be removed and disposed of by a licensed waste control operator.
It is not an offence to have Japanese Knotweed on your land and it is not a notifiable weed. However, under Section 14(1) and (2), of the Wildlife and Countryside Act 1981 it is a criminal offence to plant Japanese Knotweed or otherwise cause it to grow in the wild. However, it is a defence to a prosecution to prove that all reasonable steps were taken and all due diligence was exercised by the landowner.
The removal, eradication and disposal of the weed may be expensive but given that it's presence can impede the sale of your property and/or affect the value, a least-risk approach is to have it removed by licensed contractors and properly disposed of.
Again, it is not an offence for Japanese Knotweed to be present on your neighbour’s land but allowing it to encroach onto your property may constitute a private nuisance under common law.
A landowner affected by knotweed growth from a neighbouring property may therefore be able to apply to court for an injunction requiring the neighbouring owner to abate the nuisance. Such a claim can also include a sum of money in damages to reflect the cost of any physical damage to the property and/or the diminution in value of the landowner's property as a result of the nuisance.