Japanese knotweed
30 January 2021

Getting to the roots of Japanese knotweed

Gardeners across the UK recoil in horror at the mere mention of Japanese knotweed, but for those readers unfamiliar with this botanical beast, suffice to say that it is one of the most pervasive invasive species in Britain. Having arrived here with no natural competitors, Japanese knotweed can grow more than a metre per month, rapidly outcompeting local flora. “Weed” seems like a misnomer for this monster, which can push through tarmac, concrete and drains. It is often found beside rivers, where it erodes the banks and increases the risk of flooding. Understandably, it is against the law to plant Japanese knotweed in the wild.

A botanical burden

Japanese knotweed could cost your charity or business more than a few split pavement slabs. If left untreated, it could damage your buildings, leading to hefty repair bills, or damage neighbouring properties, which could lead to legal action against you if the root of the problem is on your organisation’s land. And if you fail to take reasonable action, you could be fined several thousand pounds. 

Identifying the intruder

So, how do you spot these green space invaders? Fortunately, Japanese knotweed has several distinguishing features. Zig-zagging, reddish stems connect lush green shield shaped leaves, which are typically around 12cm long, with a flat edge where they join the stem. The foliage grows from thicker, bamboo-like, purple speckled stems, and the roots are covered in tiny white shoots and are bright orange inside.

Stemming the spread

If you find this pesky plant on your land, you must prevent it wandering into the wild. This will require aggressive action, and you may prefer to employ professionals. If you notice Japanese knotweed in a neighbour’s garden, chat to them directly before contacting the council, as they may be dealing with it already.

Here are a few termination techniques:

  • Shift it – dig up and dispose of the weed at a specialist waste site. Check they have a permit for invasive plants, and tell them what you are bringing so they can prepare. Spray down your vehicle afterwards and check for any plant remains left behind.
  • Spray it – use approved herbicides only, follow hazardous substance health and safety advice, and re-spray regularly. It can take three years of treatment before deep roots become dormant.
  • Bury it – if you can dig a hole five metres deep (no easy feat!), you can bury Japanese knotweed on site, providing all remains are wrapped in an impenetrable membrane.
  • Burn it – as a business, you must tell the Environment Agency and your local council before you burn Japanese knotweed. Any surviving remains must be buried or removed as mentioned above.
  • Bring in the experts – ensure your chosen specialist belongs to a certified trade body such as the INNSA or Property Care Association

Prevention is the best protection

Unfortunately, many buildings insurance policies don’t cover damage to your own property by Japanese knotweed. Given the risks, it’s best to remove it immediately. You’ll have to cover the treatment costs, but these should still be cheaper than property repairs.

Your neighbours and your liability

If the weed breaches your borders and a neighbour wants to claim for damages, this would come under Public Liability Insurance and the neighbour must prove that your organisation has been negligent. The mere existence of Japanese knotweed does not automatically imply negligence, but if you were aware of it, you must prove that you’ve taken appropriate action. 

If your Scout group is approached by a third-party with a claim, contact Unity and we’ll process it for you.  

Other organisations or people should contact their building insurance provider for assistance.

To find out more about building insurance and third-party liabilities, give our team a call on 0345 040 7702.