Plant Decoded
By 
Short answer
Not in any way you’d notice. Houseplants can remove some pollutants in small sealed chambers, which is where the idea came from. But a 2020 review worked out you’d need somewhere between 10 and 1,000 plants per square metre to match what ordinary ventilation already does. Open a window instead, and keep plants because you love them.
Where the idea came from
In 1989, NASA scientists studied whether plants could help clean the air in sealed spaces, like future space stations. They put houseplants into small sealed chambers, added chemicals like benzene and formaldehyde, and watched the levels drop over a day or so.
The results were real. But lists of the “best air-purifying houseplants” spread from there, and somewhere along the way “plants reduce pollutants in a sealed box” became “a peace lily will clean your bedroom”.
Why a sealed chamber isn’t your living room
The test chambers were tiny and airtight. Your home isn’t. Air leaks in and out through doors, windows, vents and gaps all the time, swapping out the air in a room again and again throughout the day.
A 2020 review took results from a dozen studies and converted them into how much clean air plants deliver in a real room. The answer: so little that you’d need somewhere between 10 and 1,000 plants in every square metre of floor to match what ordinary air exchange already does.
Even in the original chambers, researchers noticed that much of the cleaning seemed to come from microbes living in the potting soil, not just the leaves.
So do houseplants do anything for indoor air?
A tiny bit. They take in a little carbon dioxide, release a little oxygen and add a touch of humidity. None of it is enough to change how your air feels or how healthy it is.
What they do seem to do is make people feel good. Plenty of people find rooms with plants more pleasant and calming. That’s a perfectly good reason to fill your home with them.
What actually cleans indoor air
- Ventilation. Opening windows, even briefly, swaps out more air than any number of plants.
- Extractor fans. Use them while cooking and showering.
- Fewer sources. Store paints and solvents away from living spaces, and don’t smoke indoors.
- An air purifier with a HEPA filter for dust, pollen and smoke particles.
For the curious
Below the surface: the maths behind the myth
The 2020 review used a measure called clean air delivery rate, or CADR. It’s the amount of pollutant-free air a device, or a plant, effectively supplies per hour. Air purifiers are rated this way, which makes it a fair comparison.
Chamber studies measure how fast a pollutant disappears in a tiny sealed space. Scale that up to the volume of a real room and the effect of one plant shrinks to almost nothing. Meanwhile, typical buildings replace their indoor air with outdoor air roughly once every one to several hours through normal leaks and ventilation. Plants simply can’t compete with that.
How sure are we?
Quick questions
Which plant is best for cleaning the air?
None of them in any meaningful amount. Choose plants that suit your light and how much care you want to give.
Do snake plants give off oxygen at night?
Snake plants take in carbon dioxide at night, but they release oxygen during the day like other plants. Either way the amount is tiny.
Are houseplants still worth having?
Absolutely. They’re beautiful, they’re good company, and caring for them is satisfying. Just don’t rely on them for clean air.
Sources
- Cummings BE, Waring MS (2020). Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies. Journal of Exposure Science & Environmental Epidemiology 30: 253–261. Read the paper
- Wolverton BC, Johnson A, Bounds K (1989). Interior landscape plants for indoor air pollution abatement. NASA technical report.
Spotted something that looks wrong? Email hello@plantdecoded.com and it’ll be checked and corrected.
