Do Indoor Plants Clean The Air?

Words by Niall McCauley


It's time to clear the air, because plants don't.

At least not as much as we’ve been led to believe! And it’s something that has somehow mistakenly become ‘common knowledge’. Don’t get me wrong, I’ve bought a plant on this basis in the past. A cute little Sword Fern, goaded on by the label saying how it’ll make my ‘air so pure’.

How did this idea become a universal truth? Well, it might surprise you to know that it started, in large part, thanks to space!


Why Do People Think Plants Clean The Air?

Back in 1989, NASA conducted the snappily titled ‘Interior Landscape Plants for Indoor Air Pollution Abatement’ study. Their goal was to determine whether plants could filter the air, paving the way for even better air quality in spacecraft.

If it worked, it could help future manned missions venture further into outer space. I can just imagine a space station filled with awesome looking plants floating in zero gravity. Think of the Instagram pics! If Instagram had existed in the late 1980’s.


The Results

Sadly, the tests were more mundane, and earthbound. NASA scientists tested a whole range of different plants, from Dracaenas to Philodendrons, to see if they could filter out harmful volatile organic compounds like formaldehyde. And many did! But a few key details have fallen by the wayside over time, the biggest being the environment the plants were tested in.


Each plant tested was contained within a small test chamber, which is very different from being in the corner of a large living room or office space. Although many could remove these dangerous compounds from the air, in reality their speed of doing so was slow. Slow enough that they couldn’t really compete against the airflow inside a


"Trees are key to counteracting carbon dioxide in the atmosphere"

We always associate fresh air with being outdoors, whether it’s amongst trees in a forest, walking through lush fields, or just being out in the garden. We know that trees are key to counteracting carbon dioxide in the atmosphere.


So much so, that large carbon-producing organisations like electricity providers and airlines offset their carbon emissions through schemes such as reforestation projects.


We can’t be blamed for assuming that plants help to make our indoor air better when they’re clearly playing such an important part globally.

"You would need approximately 10 plants per square foot."

The Truth Comes Out

Skip forward to 2019 and two scientists, Bryan Cummings and Michael Waring conducted their own study to see whether the results reported by NASA and other scientists actually translated into real-world effects. Their results weren’t what people expected to hear.


They found that to effectively remove harmful compounds from the air, you would need approximately 10 plants per square foot. Yup, you heard that right. 10 plants. Per. Square. Foot! Now I won’t lie, that many houseplants sounds epic and if I had the budget, that’s a challenge I’d totally take on. Alas, it’s probably not the most practical of houseplant setups.


Whether we’re talking about a plant in a NASA test chamber, or vast forests, it’s all about scale. Plants can clean the air of harmful compounds, but only in a very small space, or you’re going to need so many plants, you may as well wave goodbye to your furniture.

Your Monstera Deliciosa might be huge, but unfortunately it still ain’t big enough to clean the air around you.

Just by being a good houseplant parent and optimising the conditions for your plants, you are benefiting at the same time.

It’s Not All Bad News

But if you’re now looking at your houseplants and seeing them as imposters that made you buy them under false pretences, I still think they’re one of the best, if not the best, ways to improve your indoor environment. Because it’s not only airborne compounds and chemicals that affect the air we breathe. There are other factors that affect our indoor environment.


Compared to the outside world, the houses we live in are dry, dusty and often airless. Just by being a good houseplant parent and optimising the conditions for your plants, you are benefiting at the same time.


Keep them watered and misted and you’re balancing the humidity levels in your home. Throw open the curtains to let the light in for your houseplants and you’ll get more sunlight yourself. Tend to your houseplants to keep them happy and you get a boost to your own happiness, because caring for something is known to improve your wellbeing. Rearrange and display them beautifully and you level up the aesthetics of your living or working space.

Selling Point

Perhaps houseplants’ ability to clean the air has been oversold over the years. But maybe we’re expecting too much when they already improve our lives largely unnoticed. By giving them what they need, plants help us bring into our environments the very things we need too, even if they don’t act like living air purifiers. As for me, I’ve decided my Sword Fern can stay. It’s doing more than enough to earn its place on the shelf!

Clay, The Contemporary Botany Company

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We lovingly curate a selection of indoor plants & handmade pots. Currently delivering all across Dublin.
When not writing for the Clay Journal, Niall fronts the young, dynamic, Irish YouTube channel, ‘Niall Gardens’. Unashamedly garden obsessed, Niall shares his passion for plants and gardening from his stunning one acre garden in the Irish countryside.
Images by:
A Butchers Hook, Clay, Oleg Magni, Bernardo Dolin