Cornflowers and poppies were once considered “difficult weeds”
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One of the most common claims in mainstream gardening lore is that weeds only grow in bad soil. Improve the fertility of your plot and the weeds will disappear. If true, this simple trick could save gardeners hours of work just by adding plant food. That’s an attractive proposition – so let’s look at the evidence.
First, what do we actually mean by the word “grass”? Rather than a closely related group of plants, “weed” is actually a catch-all term for any species growing where humans don’t want it. If that sounds arbitrary or cultural to you, that’s because it is.
Many notorious weeds in some contexts live a secret double life as prized plants in others. Take the dandelion. It is easily the most common species on weed killer packaging in the UK. Yet in Singapore, where dandelions are considered exotic, I’ve seen seeds sell for nearly $100 at online auctions.
All five in fact the most invasive plant species identified in a recent global study were originally introduced as garden plants. This blurs the clear distinction between “weed” and ornamental plant, probably to the point where the word itself begins to lose much of its meaning.
What many commonly cited weeds have in common is a luxuriant growth habit. Their ability to establish quickly, reproduce readily, and tolerate a wide range of conditions is precisely what allows them to appear where they are not wanted. These characteristics often make them the first plants to colonize disturbed or neglected land—places where other species struggle to gain a foothold. But tolerating bad conditions is not the same as preferring them.
In fact, many classic weeds actively prefer rich soils. For example, nettles are strong associated with nutrient-rich soil. Dandelions too it thrives where there is enough nitrogennot where fertility is low.
So where did the idea that weeds signal infertility come from? Like many gardening myths, this one contains a kernel of truth. Improving soil fertility can allow a wider range of plants to grow and reduce the competitive advantage of the hardiest pioneer species. This effect was demonstrated on farmland in 20th century Europe, when the use of synthetic fertilizers increased. Vital grasses have finally been able to defeat troublesome weeds such as cornflowers and poppies – to the extent that some of these species are now on the verge of extinction in the United Kingdom. The great irony is that these very same plants are now very fashionable wildflowers.
Do I know where that leaves us? As our views on plants are constantly changing, it seems fair to say that weeds are not so much a reliable indicator of soil quality as they are a reflection of human whims and preferences.
These articles are published weekly at
newscientist.com/maker
James Wong is a botanist and science writer with a special interest in food crops, conservation and the environment. A graduate of the Royal Botanic Gardens in Kew, London, he shares his tiny flat with over 500 houseplants. You can follow him on X and Instagram @botanygeek
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