Houseplants do not measurably clean the air in a normal home. The idea traces back to a 1989 NASA report, and the report is real. It measured something narrower than the shopping lists built on it. Below we set out what the study did, what a 2020 review and the US EPA concluded, and which of the tested plants are safe around pets.
If you bought a plant to fix a smell, damp or a headache, the useful step is to find the source. A plant is still worth growing for its own sake.
What the 1989 NASA study actually did
The report is Interior Landscape Plants for Indoor Air Pollution Abatement by B. C. Wolverton, Anne Johnson and Keith Bounds. It was a two-year project funded jointly by NASA and the Associated Landscape Contractors of America (ALCA). The authors were interested in sealed buildings and future sealed space habitats.
The method, as the report describes it:
- Sealed chambers. Each plant was sealed in a Plexiglas chamber. Two chambers measured 0.76 × 0.76 × 0.76 m (30 × 30 × 30 in). Two larger ones were 1.53 m (60.5 in) tall.
- One chemical at a time. Benzene, trichloroethylene (TCE) or formaldehyde was injected, then sampled at the start, at 6 hours and at 24 hours.
- Constant light and a fan. Grow lights ran throughout the test, and a small fan circulated air inside the chamber.
- High doses first. In year one, plants faced about 15–20 parts per million (ppm). The authors wrote that these levels were “far above the levels commonly found in indoor atmospheres.”
- Lower doses in year two. Benzene and TCE were retested at under 1 ppm with gas chromatography.
- Controls. Empty sealed chambers checked for leaks. Pots of the same potting soil without a plant checked what the soil removed.
Two findings matter for anyone reading plant rankings. First, potting soil alone removed some benzene. In the low-concentration tests, the soil control removed 20.1% of the benzene in 24 hours. Second, the authors concluded that “the plant root-soil zone appears to be the most effective area” for removal, and that foliage over the soil reduced it. Their summary recommended activated carbon filters with fans “as an integral part” of any plant-based system.
The plants NASA tested, with ASPCA pet status
The report used nursery plants in their original pots and potting soil. Plant names below follow the report. The table numbers show where each plant appears in the report’s results. Pet status is from the ASPCA plant database.
| Plant (as named in the report) | Botanical name in report | Report tables | ASPCA, dogs and cats |
|---|---|---|---|
| Bamboo palm | Chamaedorea seifrizii | 1, 2, 3 | Non-toxic (ASPCA entry lists Chamaedorea elegans) |
| Chinese evergreen | Aglaonema modestum, ‘Silver Queen’ | 2, 3, 5, 8 | Toxic: insoluble calcium oxalates |
| English ivy | Hedera helix | 1, 2, 3, 5, 6 | Toxic: triterpenoid saponins |
| Ficus | Ficus benjamina | 4 | Toxic: ficin and ficusin |
| Gerbera daisy | Gerbera jamesonii | 1, 2, 4 | Non-toxic |
| Janet Craig | Dracaena deremensis ‘Janet Craig’ | 1, 2, 3, 5, 6, 7 | Toxic: saponins (Dracaena entry) |
| Warneckei | Dracaena deremensis ‘Warneckei’ | 1, 2, 4, 5, 6 | Toxic: saponins (Dracaena entry) |
| Marginata | Dracaena marginata | 1, 2, 3, 5, 6, 7 | Toxic: saponins |
| Mass cane | Dracaena massangeana | 1, 4 | Toxic: saponins (corn plant entry) |
| Mother-in-law’s tongue | Sansevieria laurentii | 1, 2, 3, 5, 6 | Toxic: saponins (snake plant entry) |
| Peace lily | Spathiphyllum ‘Mauna Loa’ | 1, 2, 3, 5, 6 | Toxic: insoluble calcium oxalates |
| Pot mum | Chrysanthemum morifolium | 2, 4 | Toxic: sesquiterpene lactones, pyrethrins |
| Golden pothos | Scindapsus aureus | 3, 5, 6, 7 | Toxic: insoluble calcium oxalates |
| Green spider plant | Chlorophytum elatum | 3 | Non-toxic (ASPCA entry: Chlorophytum comosum) |
| Heart leaf philodendron | Philodendron oxycardium | 3 | Toxic: insoluble calcium oxalates |
| Elephant ear philodendron | Philodendron domesticum | 3 | No entry for this species; other philodendrons are listed as toxic |
| Lacy tree philodendron | Philodendron selloum | 3 | Toxic: insoluble calcium oxalates |
| Banana | Musa oriana | 3 | Non-toxic (ASPCA entry: Musa acuminata) |
| Aloe vera | Aloe vera | 3 | Toxic: saponins, anthraquinones |
Only four of the 19 are listed as non-toxic to dogs and cats. If you share your home with pets, our pet-safe plants guide sorts more options by light. The toxic plants guide lists the clinical signs.
Why a sealed chamber does not predict a room
A chamber result answers one question: how fast did one plant lower one chemical in a small, closed box? A home differs in three ways:
- Air is replaced. Outdoor air enters through windows, doors, vents and gaps. The EPA notes that infiltration “occurs in all homes to some extent.”
- Sources keep emitting. Paint, cooking, furniture and cleaning products release chemicals continuously, not as a single injected dose.
- Volume is far larger. A room holds many times the air of a chamber under 1 m³.
In 2020, Bryan Cummings and Michael Waring of Drexel University reviewed 12 published chamber studies. They converted 196 experimental results into a clean air delivery rate (CADR), the metric used for air cleaners. The median for a single plant was 0.023 m³ per hour. On that basis, a building would need 10 to 1,000 plants per square metre of floor to match the removal that normal outdoor-to-indoor air exchange already provides. Their title states the conclusion: Potted plants do not improve indoor air quality.
The US EPA reaches the same point. Its indoor air page says there is “currently no evidence, however, that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices.” It adds a practical warning: overly damp soil “may promote the growth of microorganisms which can affect allergic individuals.”
What to do instead
The EPA lists three strategies, in order of usefulness for most homes:
- Source control. The EPA says this is “usually the most effective way” to improve indoor air. Remove the source, seal it, or adjust it, such as a gas stove.
- Ventilation. Open windows when weather allows, and use bathroom and kitchen fans that vent outdoors. Ventilate hardest during painting, sanding, soldering or cooking.
- Air cleaners and filtration. These help with particles. The EPA notes that air cleaners are generally not designed to remove gaseous pollutants, and that their performance depends on maintenance.
Keep plants for the right reasons
Choose a plant for the light you have, the care you can give and the animals in your home. Water by checking the potting mix, not by schedule. Empty saucers so the soil does not stay soggy. That habit also addresses the EPA’s point about damp soil and allergies.
For the peace lily specifically, see what the NASA study measured for peace lily. For watering technique, see our watering guide.
References
- Wolverton, B. C., Johnson, A., Bounds, K. (1989). Interior Landscape Plants for Indoor Air Pollution Abatement. NASA Technical Reports Server, 19930073077.
- Cummings, B. E., Waring, M. S. (2020). Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies. Journal of Exposure Science and Environmental Epidemiology 30(2):253–261. PMID 31695112.
- US Environmental Protection Agency: Improving Indoor Air Quality
- ASPCA Animal Poison Control Center: Bamboo Palm, Chinese Evergreen, English Ivy, Weeping Fig, Gerber Daisy, Dracaena, Madagascar Dragon Tree, Corn Plant, Snake Plant, Peace Lily, Chrysanthemum, Golden Pothos, Spider Plant, Heartleaf Philodendron, Lacy Tree Philodendron, Banana, Aloe