Do houseplants actually improve air quality?


Most of us have been spending a lot more time at home these past couple of years, prompting us to ask questions about the quality of the indoor air we breathe. Pre-COVID reports show that we Brits spend more than 90 per cent of our time indoors, where levels of some toxins can be up to five times greater than they are outdoors.

The internet is full of claims that houseplants can help, with just about every wellbeing site boasting its own top-10 rundown of the most powerful air-purifying plants. But is there any truth to the claims?

Unfortunately, not much. Most of the articles, if they cite any evidence, point to a NASA study from 1989. Back then, scientists were investigating plants’ ability to remove harmful chemicals called volatile organic compounds (VOCs) from the air of sealed environments such as space stations. In our homes and offices, sources of VOCs include paints, varnishes, furniture, carpets and printers. The study found that over a 24-hour period, several species of plants could indeed remove up to 70 per cent of one, or more, of the three VOCs tested.

But the results don’t translate well to the typical home or office, according to a 2019 review that revisited the NASA data, along with 11 other studies from the decades since. For starters, the experiments typically used fans to waft the VOCs over the plants, and carbon filters to collect them – setups that most of us don’t have in our homes.

More importantly, the plants were placed in small, sealed chambers. But the buildings we live and work in are surprisingly leaky. In fact, the researchers estimate that you’d need to squeeze between 10 and 1,000 plants into each square metre of your home to approach the rates of VOC removal already happening through passive indoor-outdoor air exchange.

Research shows that houseplants do have a range of other benefits, however. They help regulate humidity. They can improve mood and boost productivity. And they look good, to boot. But if you want to freshen up the air in your home, your best bet is to buy an air purifier with a high-quality filter or – depending on where you live – to open a window.

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Asked by: Sam Nicholls, via email

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