Japanese Knotweed Matters
16 May 18

Japanese Knotweed Matters

It can crack tarmac, block drains, increase erosion, undermine foundations and invade buildings. Its presence can be enough to cut a property's value by up to 20% or prevent a mortgage lender approving a loan.

So why is it even here?

During the rapid development of the railways in the 19th century, Victorian engineers were faced with looking for ways to disguise – or stabilise – the increasing number of railway embankments. Using Japanese knotweed ticked all the boxes.

However, growing at an alarming rate of 10cm per day (in summer), it has proved to be hugely invasive, causing serious issues for land and property owners. According to researchers from the University of Leicestershire, sharing cuttings and disposing of unwanted plants were largely responsible for the issue.

How do I recognise Japanese Knotweed?

Like most plants, Japanese knotweed grows most during the warmer months between April to October, although warmer winters and regular rain has meant that its growing season has extended. Look out for:

  • Red tinged shoots when it first appears
  • Large spade shaped leaves
  • White flowers in summer
  • A hollow stem
  • Autumn sees it dying back leaving brown stems

This factsheet prepared by the Non-native Species Secretariat (NNSS) may help.  Alternatively check out this RICS video.


Japanese knotweed is classified as controlled waste under the Environmental Protection Act 1990, which implemented strict rules for its disposal.

As most gardeners are aware, pruning or cutting back can encourage growth in normal circumstances. Cutting knotweed stems cannot just accelerate growth, it can cause it to spread outside the confines of your land or building.

Chemicals can help; however, it can take up to 5 years to take effect. Check out gov.uk for further information on safe disposal.

Worryingly, recent research conducted by scientists at Swansea University has indicated that total eradication is not possible. However, following one of the UK’s most extensive field trial at Taff’s Well, which included testing all 19 known methods of controlling the plant, the team believes it has found the best way of treating the plant in the long term. To be effective, getting the right balance of chemicals will be important, but timing is also key.  The team found that applying the right herbicides at the right time of the year, reduced the quantity of chemicals required which in turn reduced the impact of the environmental.

Your responsibilities as a land or property owner

Whilst you are not legally obliged to remove knotweed from your land, you have a duty of care to prevent it from spreading. Equally, it’s not acceptable for your neighbours (domestic or commercial) to ignore (or refuse) to deal with the issue.

Under the 2014 Anti-Social Behaviour, Crime and Policing Act, local councils or police forces can issue a Community Protection Notice (CPN), forcing neighbours to take action, and fining them if they don't.

In June 2017 Network Rail was ordered to pay damages for the nuisance caused to two homeowners by its failure to control Japanese Knotweed. The Court of Appeal is expected to provide an important precedent on who should pay if a landowner allows knotweed to encroach on somebody else's property shortly.

Is it near you?

In 2012, the Environment Agency, Scottish Natural Heritage, the Scottish Environment Protection Agency and Natural Resources Wales launched a Plant Tracker project. Many thousands have downloaded the APP, which has identified over 6,000 reported instances of Japanese Knotweed. Click here for more information about reports local to you (or a property you may be interested in). Bear in mind, whilst this map is useful, it is not a guarantee that Japanese knotweed it not present, it could be that it has not been reported.

Our advice?

Notwithstanding CPN notices and complicated issues over disposal, lenders have different policies on dealing with its presence. Undoubtedly it will cause disruption and delay to a building project.

So, our advice? If you’ve discovered Japanese Knotweed anywhere on your property, or your building project, you should contact a Surveyor or specialist to assess the situation.

Contact us today, we’re happy to help.

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