What is a Weed?

One person’s weed is another person’s wildflower.

For the first two decades of my adult life, I neither rented nor owned a single sod of earth that was not covered either by concrete or bricks and mortar. Gardening was an abstract concept to me; the glimpse of a world in which peppering one’s speech with the odd word or two of Latin was not considered pretentious.

Eventually swapping a metropolitan lifestyle for suburbia, I found, like many, considerable solace in searching for any vestige of green on the ends of my mud-stained digits.

What I found was that I had cultivated the happy knack of persuading certain types of plant to take root which more experienced gardeners derided as weeds. As I set about removing them, I wondered: what is it that characterised a weed?

Was it, as Ralph Waldo Emerson defined in his essay, The Fortune of the Republic,“a plant whose virtues have not yet been discovered”? Or is it just a case, as the Oxford English Dictionary rather dismissively defines it, of “a wild plant growing where it is not wanted, especially among crops or garden plants”— in other words, the wrong plant in the wrong place at the wrong time?

Characteristics which define a weed include their ability to establish themselves quickly, popping up almost in the blink of an eye. Adept at spreading, they either put out so many seeds that some are bound to take root, or reproduce directly without using seeds at all.

Weeds can grow in the more inhospitable areas that those plants we deem to be desirable would struggle to get a foothold in. Even if you think you have eradicated them, some produce seeds that lie dormant for a long time until conditions are conducive for them. Simply scratching the surface of the soil can cause them to leap into life.

Clearly, until Homo sapiens started cultivating plants in earnest in a systemised fashion, the distinction between a plant that was potentially useful and one that was to be actively discouraged was a bit pointless. However, there is archaeological evidence to suggest that once the earth was first broken by a primitive hoe it provided an open invitation to weeds to take root, particularly those adapted to thriving in naturally disturbed habitats.

Even today agricultural weeds are a leading cause of crop loss, accounting for upwards of a 10% reduction in global crop production.

If you go off the coast of modern Israel, you will find the now submerged land of Atlit Yam, a gorgeously structured, thriving coastal settlement from nine thousand years ago. Plant material from that time has been preserved by the seawater, with several other remains, such as seeds for cultivated crops, like durum wheat, figs, chickpeas, and herbs. Thirty-five weed species were found, five of which are known as obligatory weeds, as they could only grow in cultivated fields.

As ahead of their times as they were, being one of the first societies with agro-pastoral-marine subsistence systems, they still had a lot to learn from gardening and planting. One of the weeds growing along their fields was mistaken as wheat because of its incredible similarity to this particular crop! This is now known as Darnel, or “false wheat”.

As you can see, within just a couple of millennia of man first sowing seeds, agricultural weeds had evolved to exploit their unique conditions, an example of what is known as fast adaptive evolution. Some even mimicked the appearance of crop plants, to more easily evade detection and eradication, like with the false wheat crop.

No matter where in the world you are, chances are you’ve come across what’s supposed to be a lake but in fact looks like a thick mat of large round leaves. The occasional lavender-pink flower identifies this species as the water hyacinth: a fast-growing plant that can rapidly cover an entire lake with vegetation, smothering anything and anyone that lives under the surface.

Water hyacinths are considered a scourge in most places, and, once they take root in a lake, are very hard to get out. Like the heads of the mythical Hydra, the moment you pull out some plants, more grow to take its spot.

Their origin, however, is much less sinister. Water hyacinths are native to South America, where they’re not considered a scourge or a menace but a beautiful water plant like the lily and lotus with many uses to boot! Local grasshoppers and bees eat enough of its seeds and leaves to keep their growth at bay. It was only when these plants were introduced to new ecosystems, without other species to keep things in balance, that they turned into “weeds”.

For millennia, the farmer’s only weapon against the invasion of weeds was the back breaking task of weeding by hand — something often delegated to children and women. Although the arrival of iron tools such as hoes made the work slightly easier, distinguishing between seedlings and weeds was problematic. Seeds were hand-scattered over the newly ploughed fields and any discernible sowing patterns were often hard to detect.

It was not until the 18th century that a solution to this problem became widely available, thanks to Jethro Tull’s grain drill used in conjunction with a harrow. The grain drill would plant the seeds in neat rows, after which the harrow could loosen the soil between the rows. Crops in the rows would be left intact while weeds on the sidelines went through a “harrowing” experience.

One of the most iconic buildings in France is the Louvre: first built as a fortress in the 12th century, reconstructed as a royal palace in the 16th, and eventually turned into a museum housing some of the world’s most famous works of art including Venus de Milo and the Mona Lisa. Buried in the midst of all the construction were once two roads, the rue des Orties-du-Louvre and the rue des Orties-Saint-Honoré, which ran just past the Louvre. Orties is French for “nettle”, and the names bear testament to the fact that the roads were built on places where weeds once stood.

Another work of art, George Boughton’s Weeding the Pavement from 1882, tells the same story: urban sprawl was creating a battleline, and weeds were no longer just an agricultural phenomenon. It became a common sight to see people crouching down on paved and open spaces in the town, picking out unwanted plants.

The presence of weeds became increasingly unwelcome in homes as well, as the fashion of growing plants for pleasure took root. Gardening is a pastime upon which Britons now spend over £7.5 billion a year — incidentally worth more than the Mona Lisa itself. Gardeners spent about as much time waging war against weeds as tending the plants they wanted!

Though weeds were considered pests while growing, they suddenly acquired an economic value when uprooted. Henry Mayhew’s survey, London Labour and the London Poor (1851), tells the stories of street vendors who sold nettles, chickweed, plantain, dandelions, and groundsel — gathered from the gardens of the rich or from parks or fields, and used as fodder for caged birds.

Although it is undignified to think of using chemical preparations as a quick fix to the weed problem nowadays, they have been around for almost two centuries.

The Journal of usual and practical knowledge, a French monthly magazine, provided its readers in 1831 with a recipe for a mixture designed “to kill grass that grows in garden alleys and between cobblestones in courtyards”. All that was needed to “purge the soil of rebel herbs for several years” was to mix twelve pounds of lime and a couple of pounds of sulphur to 60 litres of boiling water. The recipe crossed the Channel and was promoted as a way of removing “very injurious as well as unsightly” plant growth from between pavement stones.

One of the most famous detective fiction writers of her time (and possibly, of ours too) is Agatha Christie, and a good part of her work dealt with poison. “Give me a decent bottle of poison,” she once said, “and I’ll construct the perfect crime”.

As a working nurse through both world wars, Agatha Christie often dealt with the very real consequences of poisoning, inspiring her crime novels. Her knowledge let her write layered stories, including the lethal dose consumptions, accurate descriptions of the time at which the poison moved, and the body’s exact reaction — something that she couldn’t have done with any other weapon.

Of course, none of these murders could have happened if there was no poison to begin with. Fortunately for Agatha Christie’s novels, weed killers such as Eureka were quite common during her time. They would be kept at hand in garden sheds, bathrooms, and kitchens, and used to eradicate unwanted plants and the occasional relative.

The world’s most widely used herbicide, 2, 4-D, was first made available commercially in 1946, although it had been developed at the start of the Second World War. Glyphosate was introduced in 1974 and soon established itself as a widely used, cheap, and popular non-selective form of weed killer.

Environmental and sustainability concerns have led to significant resistance to the excessive use of chemically based weed killers. There is a growing recognition that weeds are not just pests but play their part in stabilising the soil, drawing up nutrients from deep in the ground, attracting pollinators and insects and, when they die, decomposing into humus, adding to the richness of the soil.

In a further step towards their rehabilitation, the Gold Medal winner at the 2021 RHS Tatton Flower Show was Sandra Nock’s Weed Thriller, a garden full of weeds. However, this presents the question, if they are in the right place and valued, are they really weeds?