It might look pretty, but getting rid of Japanese knotweed can be an ugly business. Since it’s introduction to the UK in the mid-19th Century as an ornamental plant, the question of how to treat Japanese Knotweed has been one leaving gardeners in a tangle. A Japanese knotweed survey can help provide the solution to this determined weed – but before calling out the experts, it can help to know what you’re dealing with. So: what is Japanese knotweed, what does Japanese knotweed look like – and perhaps most importantly: what damage can it do to your garden?

What Is Japanese Knotweed?

Japanese knotweed is a voracious non-native invasive species that can spell trouble for your garden. It’s latin name is Fallopia japonica – although some scientists refer to it as Reynoutria japonica, or Polygonum cuspidatum from its plant family name, where ‘Poly’ means many, and ‘gony’ is from the Greek for ‘knee’, giving ‘many jointed’. In Japan, the plant is also known as ‘itadori’ (“take away pain”) owing to its use in traditional medicine – although for many gardeners this is something of a misnomer!

Identification

If you suspect a Japanese knotweed problem in your garden, it may be time to do a little horticultural detective work, particularly as there are several plants not dissimilar in appearance (this guide can help with identification).

With it’s creeping roots, Japanese Knotweed  is a rapidly-growing, and incredibly strong clump-forming perennial with dense and tall stems, identifiable by dense, bamboo like stems with purple speckles projecting from rhizomes deep within the ground which can grow to over 7ft (2.1m).

Branches protrude from nodes along the length of these stems – and by late summer the plant produces creamy white flower tassels and heart or shovel-shaped leaves up to 14cm (5.5 in) in lengths forming a zig zag pattern across the stems.

In winter, the plant dies back, leaving dry stems standing in the ground for many months – but don’t be fooled: this dormant weed inevitably returns in spring to wreak havoc on the garden once more, as reddish-purple fleshy shoots begin to emerge from bright pink buds developing at ground level – where again, these turn into shoots.

Tracking It Down

Japanese knotweed can be found in:

  • Beds
  • Borders
  • Roadsides
  • Between paving slabs
  • Riverbanks
  • Derelict land

The Willful Weed

As with many other non-native invasive species, the role of Japanese knotweed is to dominate other native species – spreading rapidly throughout the garden and suppressing everything in its path. It’s not just vegetation either: this ruthless plant has even been known to cause structural damage to stone and brickwork.

Removing The Culprit

Removing Japanese knotweed by hand can be a strenuous, difficult and time-consuming business – even when using chemical weed repellents. It usually takes between three and four seasons to completely eradicate Japanese knotweed using standard weedkiller (professional contractors will have access to more powerful solutions which can reduce this period by up to 50%).

Weedkillers

For many gardeners, the most effective way to tackle small affected areas is by using a glyphosate-based weedkiller, ideally designed to kill Japanese knotweed. Instructions on the label normally advise that the weedkiller be applied directly to a foliar spray or to the cut canes.

Following treatment, Japanese knotweed may produce bushy regrowth with small leaves 3ft (20inches or 50-90cm) in height the following spring. Although this change in appearance signifies the weedkiller is working, it is imperative to then treat this re-growth.

If using weedkiller, take care to follow instructions to maximise the effectiveness of the product while minimising risks to the surrounding environment including other people, pets and wildlife including the green parts of other plants.

While homeowners may consider controlling it themselves if it is a small isolated clump, traditional cultural control methods can present a number of problems.

The Long (Stem) Of The Law

Japanese knotweed has proved to be so problematic here in the UK that it is now under legislation, with specific guidance on treatment and removal.

According to provisions made within Schedule 9 of the Wildlife and Countryside Act 1981, it’s an offence to cause Japanese knotweed to grow in the wild.  Fly tipping of Japanese knotweed should be reported to the Environment Agency (freephone 0800 807060).

Property Ownership

Buying (or selling) a house is a stressful enough business without the unpleasant discovery of a non-native weed rampaging through the garden. Both prospective and current property owners should follow proper guidance regarding Japanese knotweed.

In an amendment to the Anti-social Behaviour, Crime and Policing Act (2014), while it is not illegal to have Japanese knotweed in your garden you should try to control it as far as possible to prevent its spread throughout the neighbourhood – as if it does this could result in increased costs, delays, potential misrepresentation claims and even  the prosecution of property owners who fail to disclose or control its spread.

As of 2013, those selling a property must state whether Japanese knotweed is growing anywhere on the premises using a TA6 form. If purchasing, your mortgage lender should assure you of complete eradication before finalising the sale using a management plan from a professional company and backed by a transferable guarantee.

For further information and advice, contact The Royal Institute of Chartered Surveyors.

Neighbour Disputes

As with all issues concerning neighbours, it is always advisable (if you feel safe to do so) to consult your neighbour in the first instance. If there is a Japanese knotweed problem in their garden it may well be the case that they are already trying to control it – or they may not even be aware of its damaging effects or the legal implications. If for any reason this is not possible, you can then escalate this to the council to discuss action under the legislation.

Call In The Professionals

It is also important to note that home gardeners cannot get an insurance-backed guarantee without using a professional contractor to help control the spread of Japanese knotweed. This is important to keep in mind if you are planning a future sale, or if your neighbour is threatening litigation due to the spread of Japanese knotweed from your garden.

Digging out the weed without professional help can create issues surrounding proper disposal, as Japanese knotweed is now classified as controlled waste under the Environmental Protection Act 1990. An alternative to disposal is to destroy it onsite by allowing it to dry prior to burning it (Japanese knotweed should never be disposed with garden waste) – but a specialist company will be better equipped to ensure proper removal and disposal at a licenced landfill.

In addition to their page on hiring contractors the RHS also has a list of resources, including where to find local help from trained professionals who can also assist with tasks such as carrying out a tree survey or an arboricultural report.