Knot the end of the world? An agent’s guide to Japanese knotweed
News of Japanese knotweed has been spreading as fast as the pesky plant. But as is common with the news, this might be making a mountain out of a molehill. So how bad really is Japanese knotweed, and what can you do about it?
Some things are so terrible, so terrifying, and so utterly ghastly, that the mere mention of them can make a potential buyer’s face turn white. And top of that list, alongside subsidence, is the discovery of Japanese knotweed. It’s like a sinister snake lurking in the bushes, ready to slither into structures, squirm through bricks, suffocate other plants, and constrict the value of a home.
With its dense clumps of bamboo-like canes rising over 2 metres tall, Japanese knotweed also grows extremely fast - as much as 10 centimetres per day according to some reports. What’s more, it’s harder to stamp out than a plague of cockroaches: its roots go deep, really deep, and new growth sprouts from creeping underground stems that remain hidden throughout the winter.
Consequently, it’s impossible to simply cut Japanese knotweed back or dig out its roots by hand. It will keep biting back like a triffid with a bad temper. And if it’s left unchecked, it could - rumour has it - burrow through walls and undermine a property’s foundations. Gulp. No wonder the organisers of the 2012 Olympic Games spent £70m over four years to control it.
But is Japanese knotweed, which has impacted 1.5 million UK properties, really as bad as billed?
The legal implications
One thing’s for certain: it’s a bad idea for sellers to conceal the presence of Japanese knotweed. In fact, they’re legally obligated to declare it via the TA6 property information form submitted during the conveyancing process. Ignorance of its existence is no excuse, either…
An accountant from London was recently forced to pay £32,000 in damages (plus estimated costs of £100,000) for failing to declare that Japanese knotweed was lurking behind a bush at the back of his garden. He claimed that he didn’t know it was there when he sold his home. But the judge ruled that the accountant’s excuse, if you excuse the pun, simply didn’t add up.
It’s therefore prudent to advise your vendors that honesty is always the best policy. It’s not only the possibility of a nasty fine; disputes can also lead to delays, increased costs, and even sales falling through down the line.
Although full disclosure will inevitably mean some hoops to jump through - a management plan must be provided for the eradication of the not-so-wonderful weed - it will be a lot less painful in the long run. In fact, buyers’ mortgage lenders will usually demand such a plan, including a transferrable guarantee, before any sale goes through.
Japanese knotweed treatments
If the worst happens, and one of your vendors does uncover the pernicious plant before (or after) they go to market, advise them to hire a professional specialist to eradicate it. This is because Japanese knotweed, other than being a stubborn little blighter, is classed as ‘controlled waste’ under the Environmental Protection Act and must be disposed of at licensed landfill sights. What’s more, sellers simply won’t get the guarantees they need if they try to resolve the problem themselves.
It’s wise to warn them upfront about the potential costs, though. It usually takes several treatments for knotweed to finally get knotted. Treatments, which are usually performed with chemicals, typically set sellers back around £2,000 to £5,000. And it can be even more expensive if excavation works are needed.
However, it’s extremely important never to cut corners. The legal ramifications can be extremely serious. Homeowners might even have to pay a neighbour’s costs if the Japanese knotweed ultimately spreads beyond their borders.
All’s knot lost?
The good news, however, is that attitudes towards the horticultural horror are slowly changing. For example, The Royal Institute of Chartered Surveyors (RICS) has recently updated its guidance and acknowledged that Japanese knotweed poses less of a threat than once assumed.
RIC’s new advice is that whilst the wicked weed can easily damage lightweight structures like conservatories, valuers and surveyors have not, in their experience, “encountered properties where the plant had actually caused damage to substantial structures, even when growing in close proximity”.
Could it be, therefore, that public fears are based on myths and scare stories rather than hard evidence? One academic study certainly suggests so: research by global infrastructure firm AECOM and the University of Leeds has found that Japanese knotweed does “no more damage” to buildings than many other garden species. Take ivy and tree roots, for example. They can play havoc with a building’s fabric but nobody pins them as particularly pestiferous.
Encouragingly, however, lenders are slowly beginning to soften their stance on Japanese knotweed. Realising that it doesn’t, in fact, rip through concrete like the incredible Hulk, most mortgage providers are now happy to proceed with a sale as long as one of those aforementioned management plans is in place.
Treatments are improving all the time, too. Take this thermoelectric device, for example, which effectively boils Japanese knotweed’s roots by shooting a 5kv power bolt into the plant. Transport for London and English Heritage have already trialled the technology because it doesn’t use the same damaging chemicals as traditional treatments.
The best approach
So, what should agents do if the dreaded, abominable weed from the land of the rising sun insidiously slips its way into property negotiations? Above all, keep a calm head (especially if everyone else is freaking out) and try to reassure all parties. The pervasive plant isn’t exactly a welcome guest at the property party but there’s no need for buyers to pull the plug. The problem can be managed.
The biggest obstacle, of course, could be the long-term stigma attached to properties that have been affected by Japanese knotweed. The science might be changing but public perceptions will take some time to catch up. And, in the meantime, this will inevitably impact what buyers are prepared to pay.
Consequently, all you can do is simply share the information above. Tell concerned buyers about the new RICS stance and talk about Japanese knotweed in terms of a persistent gardening problem rather than an existential threat to a home’s foundations. You could even draw a comparison to bamboo, which can be even more problematic: bamboo roots can travel 30ft underground and sprout up in neighbours’ walls, causing chaos and untold damage, and yet its reputation is relatively benign.
Finally, if the existence of Japanese knotweed is still too much for your buyer to swallow then you could always try appealing to their stomach: knotweed is rich in minerals, has a long history of being used in traditional medicine, and it’s a super-tasty food that supports heart and brain health. If you can’t dig the stuff out, you could always try to eat your way through it.