Why We Must Learn to Love Weeds - WSJ.com

Coco Grass: Known to attack golf courses, it's been called "the world's worst weed." It mostly spreads by a network of underground tubers.

June is the thick of the weeding season. Maybe also the time that we feel a sneaking admiration for, say, the bindweed, an exquisite white-flowered morning glory, and its tenacious powers of survival. It is a good time, then, to ask why we demonize weeds—and why they are there in the first place.

The best-known and simplest definition of a weed is "a plant in the wrong place," that is, a plant growing where you would prefer other plants to grow, or sometimes no plants at all.

Minden Pictures

Cogon Grass: The hardy native Asian species was first brought to the U.S. as packing material in shipping crates. It has spread throughout the Southeast.

But it's a coarse definition and raises the question of what is the "right place" for a plant. It would be hard to imagine a more proper location for ash trees than natural, temperate woodland, but foresters call them "weed trees" when they grow among more commercially desirable timber—and, perhaps, because the ash's effortless regenerative power puts in the shade the forester's harder-won achievements.

And the criteria for weediness can change dramatically with time. An early settler in Victoria, Australia, remembered how a fellow Scottish immigrant changed from being a nostalgic botanical reminder of the old country to an outlawed invader: "One day we came upon a Scottish thistle, growing beside a log, not far from the stable sheds—a chance seed from the horse fodder, of course…. This was carefully rolled in a piece of newspaper and put under a stone. In a few days it was in a beautifully pressed condition and was shown round with great pride. No one thought that, some 20 years later, the thistle from Scotland would have spread in the new land, and become a nuisance, requiring a special act in some shires and districts to enforce eradication from private properties."

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Grant Heilman

Kudzu: This invasive climbing vine can grow a foot a day. It's known as the "vine that ate the South," but it's now managed to reach all to way to New England.

Other definitions have stressed other kinds of cultural inappropriateness or disability. Ralph Waldo Emerson opted for usefulness and said that a weed was simply "a plant whose virtues have not yet been discovered." This is a generous and botanically friendly idea, suggesting that reprieves may still be possible for the condemned. But virtues are in the eye of the contemporary beholder. Large numbers of plants were regarded as useful once, only for their virtues to go out of fashion or prove to be bought at great collateral cost.

Toxicity is seen as another ugly and undesirable trait. The most notorious weed in the United States is poison ivy, whose impact has been immortalized in a Leiber and Stoller ditty from 1959, one of a small group of popular songs to be titled after a weed (Elvis recorded Tony Joe White's "Poke Salad Annie," for example). In the lyrics, poison ivy is likened to a scheming woman, who'll "get under your skin," whereupon—and it's one of the great rhyming couplets of pop music—"You're gonna need an ocean / Of calamine lotion." In fact, calamine can hardly cope with the effects, which are florid and quite out of proportion to what is usually the briefest of encounters. Just the softest brush with a broken leaf can cause nightmarish effects on the skin. It goes red, blisters and itches uncontrollably.

Grant Heilman

Field Horsetail: The native perennial has been used for polishing objects and to make dye for clothing, and it's a common snack for grizzly and black bears.

Yet, in the shadows of this understandable wariness about species that can kill us off, a less rational attitude is lurking. Some plants become labeled as weeds because we morally disapprove of their behavior. Parasites have a bad name because they exploit the nutrients of other plants, regardless of whether they do any real harm in the process. Ivy is vilified as a parasite without even being one. It attaches itself to trees purely for physical support and takes no nourishment from them. Big tufts can indeed do damage by their sheer physical weight, but the myth of the sap-sucker—the vegetable vampire—is a much more satisfying basis for demonization.

Houston has its own high puritan criteria. In that space-age city, bylaws have made illegal "the existence of weeds, brush, rubbish and all other objectionable, unsightly and unsanitary matter of whatever nature covering or partly covering the surface of any lots or parcels of real estate." In this litany of dereliction weeds are defined as "any uncultivated vegetable growth taller than nine inches"—which makes about two-thirds of the indigenous flora of the entire country illegal in a Houston yard. The U.S. Department of Agriculture, struggling to find some unifying principle behind its own pragmatic blacklists, admits that "over 50% of our flora is made up of species that are considered undesirable by some segment of our society."

Andre Karwath

Common Daisy: The low-growing Bellis perennis, with small flowers, is mostly found on lawns in northern climates. Mow them down—and they grow right back.

All of these definitions view weeds entirely from a human perspective. They are plants that sabotage human plans. They rob crops of nourishment, ruin the exquisite visions of garden designers, break our codes of appropriate behavior, make unpleasant and impenetrable hiding places for urban ne'er-do-wells. But is it conceivable that they might also have a botanical, or at least an ecological, definition?

I don't mean by this that they might in some way be close biological relatives to one another: Plants tagged as weeds belong to every botanical group from simple algae to rain-forest trees. But they have at least one behavioral quality in common: Weeds thrive in the company of humans. They aren't parasites, because they can exist without us, but we are their natural ecological partners, the species alongside which they do best.

Weeds relish the things that we do to the soil: clearing forests, digging, farming, dumping nutrient-rich rubbish. They flourish in arable fields, battlefields, parking lots, herbaceous borders. They exploit our transport systems, our cooking adventures, our obsession with packaging. Above all, they use us when we stir the world up, disrupt its settled patterns. It would be a tautology to say that these days they are found most abundantly where there is the most weeding; but that notion ought to make us question whether the weeding encourages the weeds as much as vice versa.

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Everett Collection

Feed me, Seymour! Audrey II, the bloodthirsty space weed in 'Little Shop of Horrors.'

The image of weeds as human familiars is a morally neutral, ecological reflection of the cultural view of them as human stalkers. But they've been companions in a more positive sense. We've had a symbiotic relationship with many of them, a partnership from which we benefit as much as the plants.

Because they are common, accessible, comprehensible, weeds were an early port of call whenever some kind of plant material was needed for domestic purposes. Weeds made the first vegetables, the first home medicines, the first dyes. Our ingenuity with them has been boundless.

The fronds of horsetail, a persistent weed of badly drained soils and lawns, are covered with tiny crystals of silica. It makes them quite abrasive, and they were once used for polishing pewter and arrow shafts. The piths of soft rush—another invader of compacted soils—were soaked in grease and used as tapers.

Many of the species we've come to call weeds also have high cultural profiles. The common daisy has more than 35 local names, and the corn poppy is the one native wild plant whose symbolic meaning is widely known, from the mournful World War I poem about the "crosses, row on row," in Flanders fields.

Mississippi Forestry Commission

A wanted poster, from Mississippi, for cogon grass. The invasive species can be found in a range of ecosystems, from sand dunes to forests.

Children, especially, notice weeds and revel in their bad reputation and loathsome properties. J.K. Rowling understands children's fascination with bizarre plants, and Harry Potter's Hogwarts Academy has an exotic and disgusting weed flora. Bubotuber is a thick, black, slug-like plant, capable of squirming and covered with pus-filled swellings, which cause boils when they touch the skin. Devil's snare winds its tendrils around any hapless creature that gets too close. Interestingly, it can be neutralized by a charm contrived from the bluebell, a "good" plant, a wild flower, not a weed.

And weeds may have one other benefit. It lurks in our folk-memory, in the practice of fallowing a field between crops, and of composting weeds to cash in on the nutrients they've gathered. My late friend Roger Deakin always used to excuse his failure to weed his vegetable patch by saying "weeds do keep the roots moist." Despite their nuisance value to us, weeds may have an ecological point. Their long existence on the planet and all too obvious success suggests that they are highly evolved to "fit" on the earth in the Darwinian sense, to find their proper niche.

Of course, weeds don't have a "purpose," least of all to deliberately scupper our best-laid plans. Like all living things, they just "are." But as we survey our long love–hate relationship with them, it may be revealing to ponder where weeds belong in the ecological scheme of things. They seem, even from the most cursory of looks, to have evolved to grow in unsettled earth and damaged landscapes, and that may be a less malign role than we give them credit for.

Grant Heilman

Corn Poppy: This weed is a symbol of wartime remembrance, thanks to a famous World War I poem: "In Flanders fields the poppies blow / Between the crosses, row on row."

In the 21st century, the specter has risen of plants that are aggressively weedy in a more fundamental way, species whose reputation is not a matter of personal whim or cultural fashion, botanical thugs that can wreck whole ecosystems as well as human crops and landscapes. The "superweed" is a favorite villain in science fiction. The seeds of some alien plant-form reach Earth, germinate in a few hours and quickly blanket the planet, or worse, hybridize with humans. Or a genetically modified crop passes on its herbicide and disease-resistant genes to wild oats, say, and creates the ultimate botanical demon, which perfectly and ironically fulfils the anthropocentric definition of a weed: a rampant plant generated by human activity.

In the real world, the superweed is already here, not as the result of extra-terrestrial invasion but of our own reckless assaults on the natural world. Sometimes a plant is turned into a weed and then into a multinational villain because humans have exterminated all the other wild plants with which it once lived in some sort of equilibrium.

Between 1964 and 1971, the U.S. sprayed 12 millions tons of Agent Orange on Vietnam. This infamous mixture of phenoxyacetic herbicides was used as a defoliant, to lay bare entire rain-forests so that the Vietcong had nowhere to hide. It is now banned under the Geneva Convention. But this outlawing was too late for the forest, which has still not recovered four decades later. In its place has grown a tough grass called cogon.

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Cogon is a natural component of the ground vegetation of southeast Asian forest. It flourishes briefly when clearings are created by falling trees, but retreats when the canopy closes again. When the trees were obliterated in Vietnam, it rampaged across the landscape. It is repeatedly burned off, but this seems to encourage it more, and it has overwhelmed all attempts to overplant it with teak, pineapple, even the formidable bamboo. Unsurprisingly, it picked up the local tag of "American weed." Cogon recently infiltrated the U.S. in the packaging of imported Asian house-plants and is now advancing through the southern states.

Other demonic weeds have been created by simple short-sightedness. In a modern twist of the adage about a weed being simply a plant in the wrong place, large numbers of species—potential garden ornaments or food crops—have been translocated, only to turn into aggressive fifth columnists. They've often been moved thousands of miles from their native ecosystems, out of reach of all the nibbling insects and indigenous diseases that usually keep them in check.

Garden Picture Library/Photolibrary

Weeds relish the things that we do to the soil: clearing forests, digging, farming. A gardener does battle, above.

Many of these cosmopolitan invaders come from the fecund sub-tropics and have a virulence quite unlike conventional weeds. Australia has been the hardest hit, with more than 2,500 immigrant species playing havoc with its native wildlife. Globally, these "invasive aliens" are regarded as the greatest threat to biological diversity after climate change and habitat loss.

Given the scale of the diaspora of plant species, it's surprising that the ultimate plant pest—some scrambling, fast-growing, leaf-smothering, all-year-round, all-habitat, all-weather devil's snare—hasn't emerged in reality and begun overwhelming every kind of vegetation from Amazonian Brazil-nut groves to Hebridean potato plots. The reason it hasn't—and is most unlikely to—is a profoundly important fact about vegetation, and it might help us to work out a modus vivendi with the weeds that we do have.

The global advance of weed species may be leading toward a more homogenized world, where specialized and local species are driven out by aggressive Jacks-of-all-places, what the political scientist Stephen Meyer calls "adaptive generalists." "There will continue to be plenty of life covering the globe," he writes in "The End of the Wild." "Life will just be different: much less diverse, much less exotic, much more predictable, and much less able to capture the awe and wonder of the human spirit. Ecosystems will organize around a human motif, the wild will give way to the predictable, the common, the usual."

This is happening already. Even by the early 20th century, many common weeds were virtually cosmopolitan. The commonest weeds of cities in Europe and North America and Australia are virtually identical. In fact, most international weeds were originally of European origin, an ironic side effect of colonial adventures.

But global trade has today put all potential weeds on a more or less equal footing. A list of the top 18 of "the world's most serious weeds," compiled in 1977, has just three European plants—fat-hen, field bindweed and wild oats. The bulk of the remainder are aggressive grasses from the tropics, including cogon at number seven, and coco grass at number one, officially recognized as "the world's worst weed."

The American poet Gary Snyder had a close encounter with botanical aliens while climbing one of the iconic peaks of the American West, Mount Tamalpais: "We're on a part-trail part-dirt fire road, going through meadows. East into the canyon side, out of the wind, it's deep forest. California Native Plant Society volunteers are along the road wearing Tamalpais Conservation Club T-shirts, rooting out stems and roots. I ask them what, they say, 'Thoroughwort, an invasive plant from Mexico.'"

Thoroughwort is a relative of the asters and is so-called because the stem appears to push through the leaves. But its name makes it feel like an emblem of the ubiquitousness of modern weeds, which have so comprehensively penetrated our world.

But the weed community shouldn't be judged by the behavior of its most aggressive members. Weeds—even many intrusive aliens—give something back. They green over the dereliction we have created. They move in to replace more sensitive plants that we have endangered. Their willingness to grow in the most hostile environments—a bombed city, a crack in a wall—means that they insinuate the idea of wild nature into places otherwise quite shorn of it.

Weeds are, in this sense, paradoxical. Although they follow and are dependent on human activities, their cussedness and refusal to play by our rules makes them subversive—and the very essence of wildness.

—From the book "Weeds: In Defense of Nature's Most Unloved Plants" by Richard Mabey. Copyright © 2010 by Richard Mabey. To be published in the U.S. on June 28 by Ecco, an imprint of HarperCollins Publishers

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Fascinating.