Are weeds a category of plants or of human reflex? Are they a cultural creation more than a biological one? We might, as house-proud gardeners or municipal jobsworths or agri-businesspeople, dream of a world without them, but we don’t often pause to think why they are there, or what our planet might be like without them. Rather brown, probably. Rather damaged and impoverished, certainly. Take out all weeds and we’d not have the wild grass that was developed into wheat and led to the birth of civilisation. We’d have no Velcro, inspired by the hooked fruits of burdock and their obstinate clinginess to dog’s fur. Gardens would have no sweet violets, or Shirley poppies, or variegated ivies. At least half the world’s medicinal substances, from gripe-water to morphine, would never have been discovered. And gone would be the child’s lingua franca of daisy chains, dandelion clocks, Chinese-burn grasses.
I’m generalising of course. Plenty of “weedy” plants have no such virtues, just as plenty of non-weeds (I’d nominate cherry laurel and Leylandii) are riddled with incipient loathsomeness. It all depends on your perspective, on what you mean by a weed. “A plant in the wrong place” is the commonest and most useful definition. But it leads to a kind of moral relativity. We tramp the lanes for blackberry bushes, and rout them from the garden fruit-plot. Poppies are sprayed out of wheat fields but patriotically revered every November 11th. One sub-set of entomologists adores buddleia, the butterfly bush (brought here as a garden shrub from China more than a century ago), as a nectar source for flying insects; another abhors the way it has formed a kind of urban forest on waste ground, shading out the habitats and forage plants of the larvae of other insects.
All weeds are trespassers of a kind, but across boundaries which are as often cultural as topographical. Their blacklists are consequently so subjective that the only really practical definition is that a weed is a plant which gets up somebody’s nose (literally, in the case of hayfeverish grasses). Plants get labelled as weeds if they’re toxic, ugly, parasitic (ie, immoral), aggressively loutish (giant hogweed) or just limp-wristedly “weedy” (chickweed). In America, the Department of Agriculture, trying to find some unifying principle behind its own pragmatic lists, admits that “over 50% of our [America’s] flora is made up of species that are considered undesirable by some segment of our society.”
The one principle on which all social segments, on both sides of the Atlantic, agree is that they are not complicit in the presence or survival of these invading organisms. Weeds are “the others”, literal or metaphorical aliens. We have no wish to know about why they seem to dog human activities so remorselessly: we just want to find ways of getting rid of the bloody things. They’re regarded as inexplicable and impertinent intruders, whose presence is quite unconnected with the way we live our lives. Ironically it’s only those fundamentalist Christians—who still regard them as the thorns and thistles with which God punished humanity’s bad behaviour in Eden—who get it right. Weeds are our fault. It’s the trashing of our metaphorical Eden over the past 10,000 years that has given them the opportunity to move out of the wild and into what we regard as our personal space.
Although any kind of plant can become a weed just by gate-crashing, the majority are species which evolved to cope with the naturally disturbed areas of the earth: on volcanic scree, along tidelines, in gale-wrecked forests. As soon as we began our human project of opening up the earth, be it with a fork, a jcb or a napalm bomb, we created replicas of these turbulent zones, which their floral natives smartly took advantage of. Nettles (native in river flood-plains) move into the similarly rich and shifty soils of human dumps and fertilised fields. Bindweed scrambles up fences as effort-lessly as if they were willow scrub in the wild. Mexican fleabane, introduced to Britain as a rockery plant from the dry hills of Central America, has escaped to become naturalised on walls, from the elegant perimeter of Merton College, Oxford, to rough drystone in the moors. Weeds are our most successful cultivated plants
And for those who are still unconvinced about their provenance, there is a story from wartime London. After the Blitz, bomb sites were colonised by an extraordinary array of weeds: 126 species in all, according to the then director of the Royal Botanic Gardens at Kew, Edward Salisbury. They included the now famous “bombweed”, rosebay willowherb; bracken carpeting the flooded nave of St James’s, Piccadilly; ragwort on London Wall; and nettles, docks, buttercups and daisies everywhere. The fascinating thing is that 75 years earlier, a well had been dug in Tottenham Court Road to serve a new brewery, just a couple of miles from what would become the epicentre of the bomb damage. And from rock layers dating from 250,000 years ago, long before the invention of either war or gardening, botanists identified the remains of just the same weeds as flourished in London after the Blitz. These palaeolithic pests were doing their best to green over another broken landscape, shattered by glaciers and herds of rootling mammoths.
I find it oddly cheering that there should be a category of plants which undertake this essential repair role. We need to deal with weeds when they directly obstruct our human affairs. But that shouldn’t stop us respecting their role as nature’s catch-crop, part of its fabled abhorrence of a vacuum, components of a kind of vegetable immune system which does its best to repel the forces of entropy and development that create barrenness. And to do this they must be smart, nimble, adaptive and mobile. The ash—called the “weed tree” by foresters when it invades their tidy plantations—that has colonised a derelict railway line on page 90 might, ironically, soon be dead from dieback. But the space it leaves will soon be filled by other “weed trees”—sycamore, from eastern Europe, maybe sumach from America—which will force us to rethink our attitude towards so-called invasive aliens. To those who would truly prefer lifeless brown earth to these opportunist green settlers, I can only suggest they book tickets for the first passenger flight to Mars. ~ RICHARD MABEY