By Wes Porter ——Bio and Archives--December 8, 2019
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Filling your house with potted plants might make you happier and more productive, but it’s not going to make the air you breathe any cleaner, wrote Carly Cassella in ScienceAlert. A critical review, drawing on 30 years of research, has once found that houseplants have little – if any – real value as air purifiers.
Shocking news indeed. But how come then that is has been advocated for three decades? It all started in 1989 with a now famous NASA study. Houseplants were placed in a small sealed chamber to discover if they could reduce the levels of volatile organic compounds (VOCs) likely to be polluting space stations. They could and did, according to NASA cognoscenti.
However, a small sealed chamber is very different from an entire home or office environment. An extensive review by a pair of researchers in the Journal of Exposure Science & Environmental Epidemiology effectively refutes the NASA findings, and virtually all those since, that suggested houseplants assure us of clean indoor air.
The shocking truth is that for a normal 140 m² house or office (1,500 ft²), you’d need 680 houseplants or five per square metre to achieve the same air flow as opening a couple of windows, avert the environmental engineers from Philadelphia’s Drexel University. “Plants are great, but they don’t actually clean indoor air quickly enough to have an effect on the air quality of your home or office environment,” says Michael Waring.
The NASA studies on indoor pollution done in 1989 recommends 15 or 18 plants in 6- to 8-inch diameter containers to clean the air in an average 1,800 square foot house. That’s roughly one plant per 100 square feet of floor space.
However, a home or office is not a sealed chamber. Air is constantly being exchanged with outside, as environmental engineers are well aware. In fact, they have a means of measuring such, termed clean air delivery rates (CADR). Other researchers have not taken these into consideration, say the latest study authors.
As for the list of alleged houseplants, those originally tested in the NASA study appear to have been added to at whim of supporters of the practice. And even in the original tests, not every plant was found to be totally effective at removing cancer-causing pollutants.
Want clean air? Just open a window, suggests Carly Cassella. During a northern winter? Or anytime in most big cities? Perhaps a commercial air purifier is the answer. But it won’t make you feel happier or more productive as will one or a positive rainforest of houseplants. As Michelle Dickinson suggests in The New Zealand Herald, “Admire them, talk to them” but don’t expect them to absorb pollutants.
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Wes Porter is a horticultural consultant and writer based in Toronto. Wes has over 40 years of experience in both temperate and tropical horticulture from three continents.