I’ve yet to meet a gardener who doesn’t have at least one problem weed. I have several with horsetail (Equisetum arvense) chief among them. But even this is a walkover compared with Japanese knotweed.
Vigorous and seemingly indestructible, it is regarded by many as “the root of all evil”. Yet, as Nicolas Seal shows in Japanese Knotweed, Unearthing the Truth, it’s only part of the story and there may yet be a use for this foreign invader.
Seal, founder of Environet UK Ltd, which specialises in dealing with Japanese knotweed (Fallopia japonica), wrote the book “to set the record straight”. The result is a comprehensive look at the history of the plant, its botanical make-up, how to identify it and what to do, if you’ve got it in your garden.
Japanese knotweed is an herbaceous perennial that’s thought to date from 125 million years ago on Mt Fuji in Japan.
It arrived in Europe in the 1840s thanks to Philipp Franz von Siebold, a German physician and planthunter, although Seal makes a case for its migration also being due to the use of soil as ballast in trade ships.
Either way it soon gained admirers, winning a gold medal in Utrecht and appearing in many of Gertrude Jekyll’s designs. In fact, it was sold commercially until a ban under the 1981 Wildlife & Countryside Act.
By then, Seal tells us, it was too late and Japanese knotweed was already making its mark, colonising ground at the expense of native plants and damaging property. Homeowners are now legally obliged to declare the presence of the plant when selling a house and allowing it to spread to a neighbour’s land can leave you open to legal action.
Its success is due to the plant’s sheer efficiency. Rhizomes can lay dormant for 20 years and will then grow from a piece as small as a fingernail, while the fact they are brittle means they will easily break into pieces if the ground is disturbed.
Add to that the fact that Japanese knotweed has more photosynthetic material per sqm than nearly any other plant and that it has developed a bio-chemical that slows growth in neighbouring plants and it’s hard not to have a sneaky admiration for it.
It’s clear that Seal, an environmental scientist and expert on Japanese knotweed, is not among those who completely condemn the plant: “. . . Japanese knotweed is only a weed when it’s found growing in the wrong place. In other situations, it might not only prove harmless and beautiful, but might even have a future value.”
That value might be in medicine – it’s been used in traditional Chinese medicine for centuries –as a fodder crop, biofuel or even as a way of cleaning up polluted ground.
“I’m confident that Japanese knotweed will one day be considered biological-gold,” he says.
Regardless of this plant’s future, its history is a warning of the dangers of neglecting biosecurity.
• Japanese Knotweed, Unearthing the Truth, by Nicolas Seal, is published by Environet, priced at £14.99. Buy now (If you buy through this Amazon link, I get a small fee. The price you pay is not affected.)
• Review copy supplied by Environet in exchange for a fair review. Images © 2018 Environet UK Ltd/Lizzie Harper
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