Do houseplants really clean the air? What the science says, and why to grow them anyway

We need to correct something we published a few years ago. The original version of this article told you to stop paying for air purifiers because five houseplants would clean the air in your home. It repeated a figure about plants removing most of the volatile organic compounds from a room, and it presented all of that as settled. It was not, and it is not. We have gone back to the research since then, and the honest answer is that a potted plant on your desk does almost nothing measurable to the air you breathe. We would rather tell you that plainly than leave the old claim up because it sold a few pots.

The good news is that the five plants we recommended back then are still five of the easiest, most forgiving houseplants you can grow in a South African home, and there are real, well documented reasons to fill your rooms with them. They just have nothing to do with formaldehyde. Here is where the idea came from, what the science actually shows, and why we still think every home should have a fern in the bathroom and a Strelitzia by the window.

Where the clean air idea came from

The whole thing traces back to one piece of NASA work from 1989. Researchers led by Bill Wolverton were looking at ways to scrub the air in sealed space habitats, and they put common houseplants into small, airtight chambers, injected chemicals like benzene and formaldehyde, and measured how much disappeared over a day or two. The plants, or more precisely the soil microbes around their roots, did remove a good share of the chemicals under those conditions. You can read the original report, Interior Landscape Plants for Indoor Air Pollution Abatement, on NASA's technical reports server, and it is worth noticing that even the authors paired the plants with an activated carbon filter in their proposed design. The result escaped the lab, lost its context, and became a list of miracle plants that has been copied across the internet ever since. Our old article was one of those copies.

What the 2019 review actually found

In 2019 two engineers at Drexel University, Bryan Cummings and Michael Waring, did what nobody had bothered to do properly: they gathered twelve of those chamber studies, 196 separate experimental results in all, and converted every one into a clean air delivery rate, the same measure used to rate a mechanical air purifier. Then they compared that to the fresh air that already leaks into a normal building through gaps, doors and windows. Their paper in the Journal of Exposure Science and Environmental Epidemiology, Potted plants do not improve indoor air quality, found that the median plant cleaned about 0.023 cubic metres of air per hour. Ordinary ventilation in a typical building swaps the air roughly once an hour. To match that with plants alone you would need somewhere between 10 and 1,000 plants for every square metre of floor. Not per room. Per square metre.

Think about what that means for an average Centurion lounge of around 20 square metres. At the kind end of the range you would be looking at 200 plants. At the other end, 20,000. Five pots on a shelf, however lush, are a rounding error. The chamber experiments were not wrong, they were simply done in a sealed box with no air exchange, which is nothing like a house with a door that opens fifty times a day. The authors ended by suggesting that future work should stop testing whether potted plants can passively clean rooms and look instead at things like wellbeing and productivity, which is where the real evidence sits.

So what does help with indoor air?

Mostly the boring things. Opening windows, which in a South African climate we can do for most of the year. Running the extractor when you cook, and cracking a window in the bathroom after a shower. Choosing low VOC paints and letting new furniture and flooring off gas in a garage or on the stoep for a few days before it comes inside. Not smoking indoors, and keeping paraffin heaters and gas cookers well ventilated, especially through load shedding when a lot of households fall back on them. If someone in the house has asthma or allergies and you want to do more, a mechanical purifier with a HEPA filter is the thing that actually moves the needle, and no amount of ivy replaces it. We would rather you spent that money knowingly than on the strength of something we got wrong.

The real reasons to grow them anyway

Having said all that, we have never had a customer regret filling their home with plants, and there is decent research behind why. A review in the Journal of Environmental Psychology, The psychological benefits of indoor plants, went through the experimental studies on how people respond to plants indoors and found that, while results were not uniform, there was real evidence for lower stress, better mood and greater tolerance for discomfort when plants were in the room. That fits what we see every day. People slow down around plants. They notice a new leaf. The small routine of checking soil with a finger on a Sunday morning is a quiet, grounding thing in a week that has very few of those.

Plants also add a little moisture to a room as they transpire. It is a small effect and will not fix a dry Highveld winter on its own, but a cluster of ferns in a bedroom does make the air feel a touch softer, and the plants do better grouped together for the same reason. And then there is the plain fact that a room with living things in it looks and feels better. A trailing pothos on a bookshelf, a big architectural leaf in the corner. That was always the honest reason, and it is enough.

Boston fern, English ivy and the money tree

Boston fern, Nephrolepis exaltata, is still the plant we would put in almost every bathroom. It wants bright but indirect light, steady moisture and as much humidity as you can give it, so a room where someone showers every day is close to ideal. Let it dry out and the fronds go brown and drop everywhere, so a drip tray under the pot and a finger in the soil every few days is the routine. It is safe around cats and dogs, which is more than can be said for the next one.

English ivy, Hedera helix, is easy and forgiving indoors and trails beautifully off a high shelf, but it is toxic to pets and mildly irritating to some people's skin, so think about where it hangs. It is on our list of plants poisonous to pets for good reason. Keep it out of direct sun, which scorches the leaves, and water when the top of the soil is dry. Outdoors in South Africa it can become a nuisance, so keep it in a pot.

The money tree, Pachira aquatica, is the one with the braided trunk and the glossy hand shaped leaves. It copes with a wide range of light, prefers bright and indirect, and is genuinely hard to kill as long as you water it sparingly. Every superstition about it bringing wealth is yours to enjoy or ignore, but it is a handsome, sculptural plant for a lightweight pot in a hallway. Whatever you have heard about it being toxic to rats, we could not find anything to back that up, so please ignore it.

Strelitzia and air plants

Strelitzia reginae, the crane flower or bird of paradise, is the one plant on this list that actually belongs to us. It grows wild along the Eastern Cape coast and SANBI's PlantZAfrica entry on Strelitzia reginae describes a tough, clump forming plant that tolerates drought and a wide range of soils, which is exactly why it does so well indoors in a bright room. Give it the sunniest spot you have, water when the pot is dry, and accept that it may not flower inside. The big paddle shaped leaves are the point. Because it gets large and heavy over time, a pot from our Lightweight Décor range makes moving it far easier, and Indoor Potting Soil gives it the drainage it expects.

Tillandsia, the air plants, need no soil at all. They perch on a piece of driftwood or sit in a small concrete dish and take what they need through their leaves. Soak them in a bowl of water for half an hour every week or two, shake them off, and let them dry upside down so water does not sit in the crown. In dry Gauteng winters lean towards weekly. They are pet safe, they cost very little, and children love them.

Pots that make indoor plants easy

Whatever you grow, the pot decides how much work it is. A drainage hole and a tray underneath means you can water properly and let the excess run out, which is the biggest difference between a plant that lasts and one that rots in a sealed ceramic sleeve. Our lightweight range gives you the look of cast concrete without the weight, so a large Strelitzia can still be moved to catch winter light. If you want to go beyond these five, our ten easy houseplants for a jungle home picks up where this list leaves off, and the houseplant care guide covers light, water and feeding for all of them. You can also check any plant's needs in our Plant Library.

So no, your houseplants are not purifying your air, and we are sorry we once told you they were. Open a window for that. Grow the plants because a room with a fern in it is a better room, because tending them is good for you in ways the research does keep confirming, and because a Strelitzia in a light concrete pot by a north window is simply beautiful. Our Lightweight Décor range is where we would start.

Frequently asked questions

Do houseplants purify the air in your home?

Not in any meaningful way. A 2019 review in the Journal of Exposure Science and Environmental Epidemiology found you would need 10 to 1,000 plants per square metre of floor to match the air cleaning that normal ventilation already provides.

Where did the idea that plants clean air come from?

A 1989 NASA study placed houseplants in small sealed chambers and measured the removal of chemicals like formaldehyde. The results were real but do not translate to a house with doors and windows.

How many plants would you need to clean a room?

For a 20 square metre lounge, somewhere between 200 and 20,000 plants, depending on the species and the study. Five pots on a shelf make no measurable difference.

What are the real benefits of indoor plants?

Research links indoor plants to lower stress, better mood and greater comfort. They also add a small amount of humidity and make a room feel more pleasant to be in.

Which of these five houseplants are safe for pets?

Boston fern, Strelitzia and air plants are generally considered pet safe. English ivy is toxic to cats and dogs, and the money tree is best kept out of reach as a precaution.