Dealing with knotweed

Yes. Japanese knotweed is the UK’s most invasive plant.If you are a developer, Japanese knotweed on a site can result in significant removal costs and extensive delays to your proposed development, as the Olympic Delivery Authority in London has discovered. As a property owner, you should be concerned that Japanese knotweed may potentially result in damage to the foundations of your building and any surrounding pavements.

 

Japanese knotweed was introduced to the UK as an ornamental plant during the 19^th Century, and spread rapidly. It is now found in most areas of the UK. Similar to bamboo, knotweed is strong enough to grow through concrete and asphalt and can grow up to 2cm per day, yet it is extremely difficult to eradicate.

 

Spraying the plant with the recommended herbicides is the most effective option for removal, although it may take years rather than months to complete. The spraying method was employed near Fareham in Hampshire and has already delayed the completion of a road by almost three years. Spraying can only be carried out during the growing season, and eradication takes multiple treatments to achieve. Many developers instead resort to the quicker method of excavation by clearing the plant material and removing a layer of soil. The safe removal of the excavated material carries its own obligations, and the excavation and disposal costs relating to the removal of knotweed can be significant.

 

Under the Wildlife and Countryside Act 1981 it is an offence to plant or ‘otherwise encourage’ the growth of knotweed. Under certain circumstances, this may include the cutting of the plant or disturbing the surrounding soil. Any Japanese knotweed plant material or polluted soil in which it has grown is likely to be classed as controlled waste and must be disposed of at a suitably licensed or permitted landfill site. Waste hauliers need to be notified that they are carrying controlled waste. The Environment Agencies Code of Practice for the Management, Disposal and Destruction of Japanese knotweed also highlights the risk of a civil claim by adjoining landowners in the event that you allow knotweed to spread from your property onto a neighbouring site.