A 2019 Drexel University study by Michael Waring and Bryan Cummings, which reanalysed data from 12 sealed-chamber experiments, concluded that matching the air cleaning of simply opening a couple of windows would take at least 10 plants per square metre of floor space, and perhaps up to 1,000. That finding sits awkwardly beside the famous NASA study, which tested 15 houseplants and reported that some removed as much as 87 percent of certain pollutants within 24 hours.
This guide to indoor plants that survive winter and clean air keeps both stories in view. Plants are lovely, can improve a room and can be kept alive through winter with a few rules from Nebraska Extension. But they are not a substitute for ventilation or an air purifier, and I will not claim otherwise.
What the NASA Study Found
A UCCE Orange County Master Gardeners page, adapted from an article by horticulture adviser Laura Pottorff, describes the NASA work. Researchers led by Dr. Bill Wolverton tested 15 houseplants against benzene, formaldehyde and trichloroethylene, and found that some could remove as much as 87 percent of indoor air pollutants within 24 hours. They suggested one potted plant per 100 square feet.
That was a laboratory result in a small sealed chamber. The next section explains why it does not translate to a living room.
What the Drexel Study Found
In 2019, Drexel researchers Michael Waring and Bryan Cummings reanalysed data from 12 sealed-chamber studies. They concluded that houseplants do not meaningfully improve indoor air quality, because ordinary air exchange from windows and heating or cooling systems moves air far faster than plants can clean it.
| Claim | Drexel finding |
|---|---|
| Plants needed to match opening a couple of windows | At least 10 per square metre of floor, up to 1,000 |
| Plants vs a typical particle air purifier | Purifier about 5,000 times more effective (Waring) |
| Do plants still help? | Psychological benefits, according to Waring |
| Biowalls (engineered plant filters) | May help remove VOCs, but need ongoing maintenance |
So keep plants for greenery and mood, and use ventilation or a purifier if air quality is a concern.
Winter Care: Light, Water and Humidity
Sarah Browning of Nebraska Extension notes that indoor light drops sharply in winter, plants need much less water and heating dries the air.
| Factor | Winter advice (Nebraska Extension) |
|---|---|
| Light | Cacti and succulents still need high light, so a cool room with a south-facing window suits them |
| Watering | A plant watered daily in summer may need only weekly watering; check the top inch of soil |
| Drainage | Use containers with drainage holes and water thoroughly |
| Humidity | Ferns, Rex begonias, Prayer Plant and Calathea need more moisture; try bathrooms or kitchens |
| Temperature | Cacti and succulents do best at 55 to 60 degrees Fahrenheit, not below 45 |
| Fertilizer | Reduce or avoid it; flush salts with Epsom salt water |
Which Plants to Choose
The Nebraska page does not name low-light plants, so I rely on its general advice: choose plants that match the light you have. Succulents and cacti suit bright windows. Moisture lovers such as ferns and calatheas suit bathrooms and kitchens.
| Plant type | Where it fits | Winter note |
|---|---|---|
| Cacti and succulents | Bright, cool windowsill | Water sparingly |
| Ferns | Bathroom or kitchen | Keep the soil lightly moist |
| Calathea and Prayer Plant | Humid spot | Avoid dry air near heaters |
| Rex begonia | Humid spot | Needs more moisture |
If a plant keeps struggling, move it, check the soil and resist the urge to water more.
Real Ways to Clean Indoor Air
If air quality is a concern, open windows when outdoor air is good, run exhaust fans while cooking and consider a purifier. For ideas on smart air monitors and ventilation, see our guide to smart home tech. Pets may chew plants, and the sources do not address toxicity, so check each plant before you buy.
