There is a belief that keeping houseplants in our bedrooms at night is dangerous because they compete with us for air, but in reality they have a negligible effect on the indoor atmosphere, says James Wong.
ONE of my favourite old-school gardening beliefs, which recently resurfaced with the explosion of interest in houseplants, is that it is inadvisable – even dangerous – to have plants in the bedroom.
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This centres around the claim that while plants take in carbon dioxide and release oxygen in the day, at night this is reversed, so they compete with us for the very air we breathe while asleep. The build-up of CO2 is a genuine problem for indoor air quality, which has been demonstrated to have health impacts, so it is easy to see where the concern stems from. But to establish whether sharing our bedroom with our plants is actually a risk to health, we have to consider three things.
Firstly, how much CO2 do plants emit at night compared with what they absorb in the day? This is tricky to answer as it depends on everything from species to light levels and even room temperature – and the research on the precise metrics in an indoor setting is pretty thin on the ground. Thankfully, in 2015, researchers at Turkey’s Kastamonu University found that large houseplants like ficus and yuccas, when sealed in glass boxes, absorb between six and eight times as much CO2 in the day as they emit at night, creating a pretty hefty net reduction over the full 24-hour period.
And the impact they had on CO2 levels overnight wasn’t exactly enormous. Ficus, for example, created an increase of 351 parts per million by morning, which kept the levels in the boxes well within the healthy range for humans.
Secondly, we should compare the nocturnal impact of plants on air quality with that of other potential competitors, such as a partner. A single human breath contains around 40,000 ppm of CO2, more than 10 times the effect a plant could have in 8 hours, so you might want to turf your partner out before your plants.
That is before we even consider that indoor plants, typically grown at light levels far lower than their ideal range in their native habitat, photosynthesise at a much lower rate, reducing impact further.
Finally – and this may sound a bit obvious – we don’t live in the hermetically sealed boxes in which these studies are carried out. Indoor air is constantly being exchanged through built-in ventilation, under doors and windows, even just from humans moving around the space. According to one recent review, you would need between 100 and 1000 plants per square metre of floor space to mimic the impact of an open window on keeping inside air fresh, given that plants remove some pollution. In conclusion, the pot plant effect in our homes is minimal in many ways.
So enjoy houseplants whenever you like, because, frankly, if sleeping near plants were bad for your health, camping in a forest would be positively deadly.
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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