I acknowledge straight away that it might seem a bit dramatic to draw an analogy with Bram Stoker’s classic novel and the eponymous hero/villain…

But it has, I hope, grabbed your attention to consider for a moment the most annoying of all Japanese knotweed’s characteristics – it is very difficult to kill! Or, to be more precise (this is where the comparison seems most apposite), when you think you’ve killed it, you almost certainly haven’t, at least not in the way you think you have…

Japanese knotweed – dead or dormant?

Of course you can kill Japanese knotweed. We are fortunate to have herbicides which can rapidly check its growth leading to senescence and death of all the green parts we can see above soil. Spray treatments used as part of Integrated Weed Management Plans need to be applied for at least two years (with more years ‘as required’, every stand of knotweed is unique in terms of resilience probably based on the ratio of biomass above/below ground) and with perseverance, this approach will eventually prevent re-growth.

When this has been verified for at least two full growing seasons, the knotweed plan is deemed to be ‘complete’ and it is often at this stage that guarantees are issued, typically for 5 – 10 years. The tricky bit starts now; that which lies in the soil (more Dracula references!) – is it really dead or just lying doggo? The answer is somewhere in between but unlike Dracula (sorry), knotweed prefers the light and it is often this that results in apparently dead knotweed rhizome fragments deciding to grow again (tillage of the soil or complete disturbance, e.g. during building works, often being the trigger).

Be clear in your knotweed Reports/Management Plans

So is this a matter of semantics? Dead or dormant or in the twilight-zone; does it really make a difference if the key objective is just to stop the plant spreading and generally causing a nuisance? Well, it all depends. The motive for raising the subject here is to encourage everyone managing knotweed to take great care with Reports/Management Plans. To make it clear that a spray treatment alone, even for a small stand of Japanese knotweed, whilst it may prevent re-growth (particularly during the guarantee period) can never be said to be the silver-bullet/the garlic bulb/the wooden stake-through-the-heart that will guarantee the entire rhizome network never rises again from its grave! In short, we shouldn’t be using terms like ‘removed’, ‘eradicated’ or ‘killed’.

From a legal perspective this is relevant both in Tort (Duty of Care) and under Contract law. If the client believes the spray treatment is a once-and-for-all solution, only later to find that they can’t dig their garden and plant some flowers/shrubs (or replace fence posts etc.) without breaching the terms of the Guarantee they will, at the very least, feel aggrieved. So rather than leaving these matters in the small print of Terms & Conditions or the legalese language of Guarantee documents, be clear and precise in the Report/Quotation:

“This is a solution to your problem which meets mortgage lender requirements but please be aware that during and following the completion of works the area affected will be subject to some limitations on use (as detailed)”.

Even better, make the Knotweed Management Plan a cradle-to-grave (last mention of the G word – promise!) proposal so that the end-of-treatment amenity value of the garden is defined and measures incorporated so the client can enjoy the full use of their asset even during the guarantee period. This could include, in addition to the spray treatments, some localised tillage/rhizome lifting; permeable root membranes; raised borders; hard landscaping etc. etc.).

“Nosferatu” may be returning to our screens on-and-off for a few more centuries yet, but let’s try to ensure that Japanese Knotweed doesn’t!

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