I AM fascinated by how culture can colour our understanding of scientific reality, even when it comes to botany. Perhaps nowhere is this more the case than with the “native plants” debate in horticulture.
The prevailing idea is as follows: because some introduced, non-native species have caused major damage to ecosystems around the world, native plants are always a better choice for the environment. This belief has become an unquestioned part of much of popular horticultural wisdom. But where is the evidence?
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In order to argue that native plants are always a superior choice, we would need to agree on a clear-cut definition of “nativeness” with objective criteria. In many geographically isolated parts of the world, such as the Galapagos, whose flora is so unique many species are found nowhere else, this may be easy to do. But does this apply somewhere like the UK, where I live? The answer is a pretty clear no.
As prehistoric glaciations have repeatedly wiped out much of UK flora, many plants seen today as invasive “non-natives” introduced by humans, such as the common rhododendron, naturally in the relatively recent geological past. Conversely, many of our most cherished “native” plants, such as cornflowers (shown above), only arrived after being by humans in the past few thousand years. The attempt to reconcile a scientific categorisation of “native” with cultural images of what is “traditional” has led most to include all plants introduced to Britain more than 500 years ago.
Even if we did gloss over issues with this arbitrary definition, we would still need data that consistently showed “native” plants were always better at supporting other “native” species than “non-natives”. Yet, while there is a wealth of science to show that a relatively tiny handful of “non-natives”, such as Japanese knotweed, have devastated some environments, there are fewer studies that make broad, like-for-like comparisons with “natives” as a whole. And one of the most comprehensive found that, contrary to much accepted cultural opinion, .
This was because although “native” plants were more frequently visited at the beginning of the growing season, “exotics” remained in flower far later in the season, providing vital support for pollinators. Following the “native equals universally superior” ideology, according to this study, would be worse for pollinators.
If we really care about the environment, we should also care about the evidence, which on this issue is far more complex and nuanced than is often discussed.
James Wong is a botanist and science writer, with a particular interest in food crops, conservation and the environment. Trained at the Royal Botanic Gardens, Kew, in London, he shares his tiny flat with more than 500 houseplants. You can follow him on Twitter and Instagram @botanygeek
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