A long-held belief in traditional gardening suggests that weeds are exclusively a symptom of infertile soil. The prevailing notion is that by simply enhancing your plot’s fertility, unwanted plants will vanish. This appealing prospect, promising less labor through the addition of plant nourishment, merits a closer examination of the evidence.
Defining “weed” is the initial step. Far from representing a distinct botanical group, “weed” serves as a broad designation for any plant species present where humans do not desire it. This definition, arbitrary and culturally influenced, reveals its subjective nature.
Remarkably, many plants notorious as weeds in certain regions lead entirely different lives as highly valued specimens elsewhere. Consider the common dandelion. It frequently features on weedkiller packaging in the United Kingdom. Conversely, in Singapore, where dandelions are viewed as exotic specimens, their seeds have commanded prices approaching $100 in online auctions.
Further blurring the lines, a recent global study identified five of the most invasive plant species globally; all were originally introduced as garden plants. This observation challenges any clear division between “weeds” and ornamental varieties, to a degree that questions the very meaning of the term “weed.”
What commonly recognized weeds do share is a propensity for rapid growth. Their capacity to establish quickly, reproduce prolifically, and endure diverse environmental conditions is precisely what facilitates their appearance in unwanted locations. These characteristics often make them the first flora to colonize disturbed ground or neglected areas, spaces where other species find it difficult to take hold. However, enduring less-than-ideal conditions is distinct from actively preferring them.
In reality, many classic weed species actively favor rich soils. Stinging nettles, for instance, are closely associated with ground abundant in nutrients. Similarly, dandelions flourish in the presence of ample nitrogen, rather than in areas with low fertility.
The origin of the idea that weeds indicate infertility is rooted in a partial truth, characteristic of many gardening adages. Enhancing soil fertility can indeed permit a broader spectrum of plants to flourish, thereby diminishing the competitive advantage held by the most resilient pioneer species. This phenomenon was observed in 20th-century European farmlands with the increased use of synthetic fertilizers. Robust grasses gained the ability to outcompete troublesome weeds like cornflowers and poppies, leading to the endangerment of these particular species in the UK. Ironically, these very plants are now highly sought-after as fashionable wildflowers.
Thus, our understanding of weeds shifts. As perceptions of plants continually evolve, it becomes evident that weeds are less reliable indicators of soil quality and more a reflection of human inclinations and preferences.
These articles are posted each week at newscientist.com/maker.
James Wong is a botanist and science writer with a specific focus on food crops, conservation, and the environment. His training at the Royal Botanic Gardens, Kew, in London, informs his passion. He shares his compact living space with over 500 houseplants. You can follow his work on X and Instagram @botanygeek.