AS A kid in 1980s Singapore, I remember my mum coming home from a fancy Korean supermarket with a brand new electric fan. Wow! The sleek plastic design. The pivoting function. To my 7-year-old self, it was like stepping into the future. What I never understood, though, was why it had a “safety timer” that would automatically cut the power after a set number of minutes.
Years later, I learned of the curious Korean belief in . Dating back to the early 20th century, the idea behind this is that falling asleep in a closed room containing a running fan carries a real risk of death due to asphyxiation. Despite the fact there is no scientific evidence to support this claim, the belief is so widespread it is cited by South Korean government bodies as a , and electric fan makers have created built-in safety switches.
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In Korea, the reality of “fan death” is seemingly not just plausible, but plain common sense. The fascinating thing about culture is that it is often invisible to those who participate in it, and of course the Western world is no exception. To me as a gardener, an everyday example of this is the practice of “crocking”.
Take a look at essentially any segment on container gardening in the media, and you will encounter the claim that placing a layer of broken pottery, or “crocks”, in the base of containers is a key step to ensure adequate drainage. This is despite the fact that soil scientists have shown for nearly a century that through layers of material with different particle sizes than through a homogenous mix.
Air pockets in the coarser material below impede the gravitational pull of the water through the finer material, meaning water tends to only percolate down across the interface when the above layer is fully saturated. This means crocking is likely to have the exact opposite of its desired effect, potentially impeding drainage rather than improving it.
But is it possible that water behaves differently in domestic flowerpots than on the vast scale of agricultural fields? Perhaps, but to date there seems to be only one study tackling this. Carried out by consumer magazine , it compared the performance of Calibrachoa plants (which are highly susceptible to root rot in soils with poor drainage) grown in a range of pots, including those lined with a layer of crocks and those without. They found adding the crocks made no measurable difference to plant growth.
Bottom line: if you are breaking perfectly good pots just to make crocks (which loads of people do), and find the whole business a bit of a faff, remember that all the scientific evidence we have to date says the practice is at best unnecessary, and at worst may even give you poorer results.
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
For other projects visit newscientist.com/maker.
