Air-purifying plants: do houseplants really clean the air?

Do houseplants clean the air? The short answer

Air-purifying plants show up on plant tags and shop listings, and the claim usually traces back to one source: a NASA study from 1989. Do houseplants clean the air in your home? Not by any amount you would notice. The NASA tests ran in small sealed boxes. Later research found you would need a room packed with plants to match what ordinary air exchange already does.

We still think plants are worth owning, just not for that reason. None of our nine plants is on the report's core list of 12. Two of them, golden pothos and heartleaf philodendron, do appear in some of its other results, and two more, neon pothos and satin pothos, share the pothos name. Our other five plants, the Swiss cheese vine, money tree, Chinese money plant, rattlesnake plant and Dieffenbachia 'Camille', don't appear in the report at all. For each plant in this guide, we say how close it comes to what NASA tested.

The plants

1. 

   Golden Pothos

   Epipremnum aureum

   The closest match we sell to a plant in NASA's report. It wasn't on the core list, but golden pothos appears in the formaldehyde, benzene and trichloroethylene results, and it was the plant inside NASA's activated carbon filter design. The report calls it Scindapsus aureus, which NC State Extension gives as an earlier name for Epipremnum aureum. It's worth owning because it's easy to grow and survives long stretches in low light, but the ASPCA lists it as toxic to cats and dogs.

   Toxic to petsLow to bright light

   Shop Golden PothosRead the care guide
2. 

   Heartleaf Philodendron

   Philodendron hederaceum var. oxycardium

   NASA's formaldehyde results include heart leaf philodendron, labeled Philodendron oxycardium, an older name for the plant we carry, now Philodendron hederaceum var. oxycardium. The ASPCA's plant list still carries both names. NASA tested it only with formaldehyde, and only in a sealed chamber. We like it for other reasons, which our guide to low light houseplants explains, but the ASPCA lists it as toxic to cats and dogs.

   Toxic to petsLow to bright light

   Shop Heartleaf PhilodendronRead the care guide
3. 

   Neon Pothos

   Epipremnum aureum 'Neon'

   Neon pothos is the same species as golden pothos, Epipremnum aureum, and NC State Extension lists 'Neon' among its named forms. NASA tested golden pothos, not Neon, so the report's numbers don't strictly apply to it, and they wouldn't change much in a home anyway. Choose it for its bright chartreuse leaves. The ASPCA lists Epipremnum aureum as toxic to cats and dogs.

   Toxic to petsMedium to bright light

   Shop Neon PothosRead the care guide
4. 

   Satin Pothos

   Scindapsus pictus

   Satin pothos is sold under the pothos name, but it's a different plant, Scindapsus pictus, and the ASPCA lists it separately from golden pothos. That can confuse things, because NASA's report used the name Scindapsus aureus for golden pothos, not for this plant, and satin pothos doesn't appear in the report. We carry it for its silver-splashed, velvety leaves. The ASPCA lists it as toxic to cats and dogs.

   Toxic to petsMedium to bright light

   Shop Satin PothosRead the care guide

What the NASA Clean Air Study actually tested

In 1989, B.C. Wolverton and colleagues at NASA's Stennis Space Center, working with the Associated Landscape Contractors of America, published Interior Landscape Plants for Indoor Air Pollution Abatement. It's the report most lists point to.

The setup was simple. A single plant was sealed inside a Plexiglas chamber. The smallest chambers were cubes 30 inches on a side, about 16 cubic feet, and the largest were twice as tall, about 31 cubic feet. The researchers injected one of three chemicals (benzene, trichloroethylene or formaldehyde) and measured what was left 6 and 24 hours later.

The core list had 12 plants: the peace lily, a Chinese evergreen, the bamboo palm, English ivy, mother-in-law's tongue (snake plant), a weeping fig, gerbera daisy, potted chrysanthemum and four dracaenas.

Chemical levels did fall in those boxes. One detail that often gets left out: the researchers concluded that the roots, the soil and the microbes around them seemed to do much of the work. The final report recommended pairing plants with a fan-driven activated carbon filter, and the plant it used in that filter was golden pothos. A sealed box with one plant and one dose of chemical is a long way from a house. In a home, air moves in and out all day and new pollutants keep arriving.

Do houseplants improve indoor air quality? What later research found

In 2020, researchers Bryan Cummings and Michael Waring asked what the chamber results would mean in an actual building. Writing in the Journal of Exposure Science & Environmental Epidemiology, they gathered 12 published studies covering 196 experimental results. They converted each result into a clean air delivery rate, the same measure used to rate air purifiers.

The median plant cleaned about 0.023 cubic meters of air an hour, which is less than one cubic foot. To match the air exchange a typical building already gets from outdoor air, they estimated you would need 10 to 1,000 plants per square meter of floor. That's roughly 1 to 93 plants per square foot.

Their title sums it up: potted plants do not improve indoor air quality. The US Environmental Protection Agency says much the same. It acknowledges reports that houseplants reduced some chemicals in lab experiments. But there's no evidence that a reasonable number of them remove significant amounts of pollutants in homes and offices.

How to improve indoor air quality

None of this means plants are a bad idea. They just can't stand in for an open window. The EPA lists three basic strategies for better indoor air, and says the first is usually the most effective:

• Source control. Remove or reduce whatever is putting pollutants into the air. Some sources can be sealed off, and others, like a gas stove, can be adjusted to give off less.
• Ventilation. Open windows and doors when the weather allows, and run bathroom and kitchen fans that vent to the outside.
• Air cleaners. Some are very good at catching particles, but most aren't designed to remove gases, and the EPA says most tabletop models are much less effective. We'd treat one as a backup to the first two.

What houseplants can do for you

The case for houseplants is simpler. Many people enjoy caring for them, and a room with something green and growing in it looks softer and more lived in. That's a real reason to own a plant, even without a statistic attached.

Plants also give you a small, steady routine: press a finger into the soil to see if it's dry, water when it is, give the pot a quarter turn so it grows evenly, snip off a yellow leaf. Some people find that kind of small, regular task satisfying, and our care guide covers the basics.

So choose a plant for your light, your schedule and your pets, not for a list. If you're new to this, start with our easy houseplants for beginners, or browse all nine plants.

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