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A roomful of plants might having you breathing easy, but according to a new study, they might not have the air-cleaning effect you previously thought they had. A 2015 study by NASA promoted this particular benefit, but researchers at Drexel University have recently found that it would take a whole lot of plants to attain the same impact as, say, an air purifier.

See, plants do clean the air—but they do so very, very slowly. So slowly that you’d need up to 93 plants per square foot of space for the greenery to be an adequate alternative to a proper ventilation system. Even if you consider yourself an up-and-coming plantfluencer, you have to admit: That’s a whole lot of pothos.

So if you’re buying plants purely for the sake of having a fresher atmosphere, you’re better off investing in a good air purifier instead (see our picks, below). That’s not to say that your monstera isn’t beneficial in other ways. Nature has repeatedly been connected to improved mental health, and houseplants are the next best thing to living in a place with lots of trees. They’re not so bad to look at either.

See more plant stories:

The Most Popular Plants of 2019 (and Their Perfect Planter Match) Buy These Under-the-Radar Plants Before They Hit It Big What Greenery to Buy, According to Your Plant Parent Personality