If you say "Japanese knotweed" to a gardening enthusiast or property developer, you might be met with the sort of hiss usually reserved for pantomime villains. But to professional forager Ross Evans, the pest plant also represents a largely untapped and abundant food source.
"It is basically rhubarb," Evans says, as he peels back the fibrous, green and red outer skin of a knotwood branch to reveal a watery light green inner with a soft flavour that crunches like apple as you eat it. "The young shoots are also great, almost similar to bamboo shoots."
As general manager at Forager Ltd, the UK's biggest dedicated wild food supplier, Evans spends much of his week trudging through the countryside in Southeast England, gathering plants the untrained eye would dismiss as foliage or weeds, but which often end up on plates in high-end UK restaurants.
During a recent excursion to show me some Japanese knotweed patches near the company's base in the Kent village of Chartham, Evans could barely walk a few metres without spotting something edible. What to me appeared nothing more than a range of clovers was in fact a collection of leafy morsels, each bursting with their own flavour.
It didn't take us long to find the Japanese knotweed. The eight-foot-high stems with green heart-shaped leaves rising above a crowd of plants weren't easy to miss.
Originally unveiled as an ornamental plant by Kew Gardens in the mid-19th century, Japanese knotweed has been extremely successful in spreading across Britain, as an interactive map from the UK's National Biodiversity Network shows. According to a 2010 study by the non-profit Centre for Agriculture and Biosciences, Japanese knotweed costs the UK economy £166 million per year, with almost £11 million spent on battling the plant along road networks and waterways alone.
A deep-rooted species that survives in the harsh volcanic regions of its native East Asia, the plant is notorious for being able to break through concrete and compromise the foundations of buildings. It is illegal to plant in the UK and once cut down, is classed as "controlled waste," meaning it can't be disposed of with domestic rubbish. Instead, it has to go to designated landfill sites that Adam Brindle—managing director of Japanese Knotweed Specialists (JKWS), a company that specialises in eradicating the plant—says can cost around £250 for an 80-litre bin bag full to be taken away.
"Your average Joe can't just dispose of this, it has to be done by professionals," he explains. "This plant can grow from just a fingernail piece of root being dropped."
It is impossible to undertake development on land infested with Japanese knotweed, with the UK Environment Agency issuing a code of practice on managing it on development sites and clearance of the plant reported to cost up to £1,000 per visible square yard. The Royal Horticultural Society has stated that eradication of Japanese knotweed added an extra £70 million to the cost of developing the site of London's 2012 Olympics.
Destroying infestations is a painstaking process, with the plant growing back despite repeatedly being sprayed with weed killer, and companies like JKWS resorting to methods such as injecting herbicide directly into the individual stems of plants, or digging deep reinforced barriers to prevent the spread of root networks.
But despite the havoc it seems to wreak wherever it emerges, there is a growing understanding that Japanese knotweed is also a food resource. Evans says a number of London chefs use it in their menus, including Pavel Kanja, head chef at West London fine dining restaurant Flat Three.
According to Kanja, one of the biggest obstacles to cooking with Japanese knotweed is the overwhelmingly negative reputation it carries.
"People would say, 'Hang on, isn't that a pest?' and be a bit confused," he says. "But once they realise it is also edible, they are fine with it."
Kanja says he has served it up as an accompaniment to beef, as well as creating a syrup that was used in a Champagne cocktail. While he doesn't have it in any dish on his current menu, he says he thinks it would be a good base for a sorbet, and can generally be used any way that rhubarb might be.
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But on the subject of whether he thinks eating it could become more mainstream, Kanja says the ongoing reputation of the plant, as well as issues surrounding its disposal pose problems.
"There seems to be this kind of legal grey area when it comes to eating it," he says. "We can always make sure we use everything we buy, but if someone just goes out and picks it to eat, what do they do with anything left over?"
On that subject, the Environment Agency has some encouraging words for any would-be Japanese knotweed feasters.
"Our expert says […] if it has been thoroughly cooked then it is safe to dispose of in domestic waste," Senior communications specialist Laura Gottelier told MUNCHIES in an email.
Meanwhile, Evans hopes that people will take a more measured view of the plant as awareness of its edibility grows.
"From one point of view, it's a problem and from the other, a valuable resource," he says. "That's the beauty of valuing things, you can turn garbage into gold."