Best Indoor Plants for Air Quality: What NASA Found and What Science Says Now

There’s no houseplant that will measurably clean the air in a normal room. NASA’s famous 1989 study showed plants removing chemicals inside small sealed chambers, but a 2020 review of the research found you’d need somewhere between 10 and 1,000 plants per square meter of floor to match the air exchange a building already gets. Grow plants because you like them, choose pet-safe ones if you have cats or dogs, and rely on ventilation and filtration for cleaner air.

This guide is research-based: we read the NASA report, the 2020 review, EPA’s technical summary and the ASPCA plant database. Our research method explains how we work.

What NASA’s 1989 study actually measured

The study behind most “air-purifying plant” lists is Interior Landscape Plants for Indoor Air Pollution Abatement (NASA-TM-101766), by B. C. Wolverton, Anne Johnson and Keith Bounds at NASA’s Stennis Space Center. It was a joint project with the Associated Landscape Contractors of America, and NASA’s interest was in cleaning the air of sealed space habitats.

Here’s how the tests worked, according to the report:

• Tiny sealed chambers. Plants went into Plexiglas boxes measuring 0.76 m (30 in.) on each side, or 0.76 x 0.76 x 1.53 m for the larger ones. Bolted lids made them airtight. The small chambers held roughly 15 cubic feet of air; a 12 x 12 ft bedroom with an 8 ft ceiling holds about 1,150.
• One plant, one chemical, 24 hours. Each test sealed a single potted plant in a chamber, injected benzene, trichloroethylene (TCE) or formaldehyde, and sampled the air at the start, after 6 hours and after 24 hours.
• The plants. The list included bamboo palm, Chinese evergreen, English ivy, gerbera daisy, Janet Craig and other dracaenas, mother-in-law’s tongue (snake plant), peace lily and pot mum. Golden pothos appeared in a separate test of a fan-driven activated carbon filter with plants growing in it.

The report’s own summary is more careful than the headlines that followed. It says the plant root-soil zone “appears to be the most effective area” for removing chemicals, and that fan-driven activated carbon filters “should be considered an integral part” of any plan using houseplants. In other words, NASA’s practical design moved large volumes of air through carbon, and the plants were there to break down what the carbon held.

What the 2020 review found

In 2020, Bryan Cummings and Michael Waring of Drexel University published Potted plants do not improve indoor air quality in the Journal of Exposure Science and Environmental Epidemiology. They took 12 published chamber studies and translated 196 experimental results into one comparable number: clean air delivery rate (CADR), the same metric used to rate air purifiers.

Their findings:

• The median single plant delivered 0.023 cubic meters per hour of clean air. That’s about 0.014 cubic feet per minute. Purifier CADRs are quoted in the tens or hundreds of cfm; our guide to what CADR is explains the scale.
• You’d need 10 to 1,000 plants per square meter of floor for plants to match the roughly one air change per hour that outdoor air already provides in typical buildings.
• The authors suggest research should move on from plants’ “(in)abilities to passively clean indoor air” to other questions, such as active biofiltration and well-being.

To put the second point in home terms: a 150 sq ft bedroom is about 14 square meters, so the review’s range works out to roughly 140 to 14,000 potted plants for that one room.

EPA reached the same conclusion. Its Residential Air Cleaners technical summary says potted plants “have been shown to be ineffective and impractical for pollutant removal,” because there’s no active airflow and the number of plants needed isn’t feasible in most homes.

Note: Neither finding says plants do nothing. In a sealed box, they and their soil do take up some chemicals. The point is scale: a home trades air with the outdoors far faster than a few pots can work.

The best indoor plants, by the measure that matters

Since no plant cleans room air in a useful way, we’d choose by what you actually live with: light, care and pets. Several plants from NASA’s list are toxic to cats and dogs, according to the ASPCA’s Animal Poison Control database.

Plant	In NASA’s 1989 list?	ASPCA: dogs and cats	What the ASPCA lists
Spider plant (Chlorophytum comosum)	No	Non-toxic	—
Boston fern (Nephrolepis exalta bostoniensis)	No	Non-toxic	—
Areca palm (Dypsis lutescens)	No	Non-toxic	—
Peace lily (Spathiphyllum)	Yes	Toxic	Insoluble calcium oxalates: mouth irritation, drooling, vomiting
Snake plant / mother-in-law’s tongue (Sansevieria trifasciata)	Yes (S. laurentii)	Toxic	Saponins: stomach upset
English ivy (Hedera helix)	Yes	Toxic	Saponins: vomiting, abdominal pain, drooling, diarrhea
Golden pothos (Epipremnum aureum)	In the carbon-filter test	Toxic	Insoluble calcium oxalates: mouth irritation, drooling, vomiting
Corn plant (Dracaena fragrans)	Other dracaenas, yes	Toxic	Saponins: vomiting, drooling, loss of appetite
Aloe (Aloe vera)	No	Toxic	Saponins and anthraquinones: vomiting, lethargy, diarrhea

If you share your home with a cat or dog, we’d pick from the top three rows. The ASPCA’s full database covers hundreds more plants by common and scientific name, so check before you buy.

Important: If your pet chews a toxic plant, call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435 (a consultation fee may apply).

Can plants make indoor air worse?

Sometimes, in small ways. Damp potting soil and saucers of standing water can grow mold, and EPA’s advice on mold always comes back to moisture control. Water only when the soil needs it, empty drip trays and don’t let pots sit against cold, damp walls. Plants also release water vapor, so a room crowded with plants can run more humid; our guide to ideal indoor humidity covers the 30% to 50% range EPA recommends.

The Cummings and Waring review also lists “negative impacts of other plant-sourced emissions” as a topic needing field research. We’d treat that as an open question rather than a reason to avoid plants.

What actually cleans indoor air

EPA’s page on ozone generators lists the proven ways to control indoor air pollution: source control, ventilation and air cleaning, and notes that air cleaning “is not generally regarded as sufficient in itself.” Here’s what each looks like at home.

• Remove or reduce the source. Store paints, solvents and fuel outside the living space, choose low-VOC products and don’t smoke indoors. EPA calls source control usually the most economical and effective step.
• Ventilate. Run the range hood when you cook and the bath fan when you shower, and open windows when outdoor air is clean. This is the air exchange that the 2020 review found plants can’t compete with.
• Filter particles. A HEPA air purifier sized for the room, or a MERV 13 filter in your HVAC system if it can take one, removes dust, pollen, pet dander and smoke particles. Our air purifier size calculator shows what CADR a room needs, and our guide on whether air purifiers work explains what they can and can’t do.
• Use carbon for gases. HEPA alone doesn’t remove VOCs or odors. If chemicals are the concern, look for a purifier with a substantial activated carbon filter; our best air purifier for VOCs guide covers what to look for.

For a full checklist, see our guide on how to improve indoor air quality.

Our take

In our view, the “NASA-approved air purifying plants” label is the most durable myth in indoor air. NASA’s work was real, but it measured single plants in sealed 15-cubic-foot boxes, and its own design added a fan and a carbon filter. When researchers converted the plant data into the same CADR numbers used for purifiers, a pot of greenery came out far too slow to change the air in a room.

We’d skip buying plants for air quality and buy them for the reasons that hold up: you enjoy them, they suit your light and they’re safe for your pets. For cleaner air, we’d put the money toward a range hood that vents outside, a good HVAC filter or a HEPA purifier. If someone in your home has asthma or allergies, talk to your doctor about which triggers matter most.