House plants do NOT purify the air.
They DO absorb toxins.
BUT
(And it’s a big but)
They also release them.
The idea that houseplants work as air purifiers is everywhere and it stems from a study conducted by NASA in 1989. I took this picture in a garden centre yesterday, so the notion is still going strong.
Not to put too fine a point on it, it’s an elaborate marketing tactic stroke scam.
If you would prefer to watch this in video form, her it is:
Before you buy a peace lily to act as an air purifier let me just run this analogy past you.
Imagine that instead of needing an air purifier you need a jar of honey. Let’s say a jar of honey costs £5 and a bee costs 20p. You don’t have £5, but you do have 50p.
So you do your research about which bee is the best for honey, you go and buy your bee, and you buy her a house and unfortunately the first bee dies because you gave her the wrong flowers so you go to buy another two, just in case bees get lonely. But no matter, you’re still £4.40 up.
After doing some initial research on bee mechanics you realise that you’re going to need a further few bees.
And now you’ve got 200 bees and you realize they’re still not going to make nearly enough honey to fill a jar. Because it turns out you’d need 1,152 bees to make ONE JAR of honey.
Do not buy bees to get honey. Do not buy houseplants to purify your air.
If you’re having fun, go ahead, but if you’re looking for them to make a significant difference to your air quality you’re going to need hundreds in a sealed house…and the research suggests even that may not have the intended effect.
So where did the whole ‘plants-purify-the-air thing come from?
It was a study done by NASA in 1989 which I’ve linked, called Interior Landscape Plants For Indoor Air Pollution Abatement.
There’s something interesting to note on page 3, which I shall include below:
This work was jointly supported by the NASA Office of Commercial Programs – Technology Utilization Division, and the Associated Landscape Contractors Of America.
Right, I’m not saying that that’s Big Houseplant, but I’m not NOT saying that. These people want consumers to value plants. In order to to get people to value a product, you must give that product purpose.
And if I wanted people to buy houseplants I’d definitely fund a study run by NASA that shows that houseplants purify the air.
Because other than serving as home decor or a hobby, house plants do not have a purpose.
What was the purpose of the study?
The reason for the study was initially nothing to do with space travel.
In the 70s when energy prices were increasing buildings were designed to be more efficient with heating and cooling – they were basically sealed units so were easier to control.
This *apparently* caused an illness called ‘sick building syndrome’ supposedly because the building materials off-gas various chemicals.
Off-gas is just a fancy (or very not-fancy) way of saying releases.
BTW, the no.1 cure for sick building syndrome (as per the NHS website) is opening a window, but that doesn’t make anyone any money.
**I will say that if you look up sick building syndrome on the NHS website, it is VERY dismissive.
They 100% think that sick building syndrome is not a thing, and the symptoms are caused by a combination of harsh lighting and stress NOT impure air.**
NASA were all like ‘sealed buildings? Houseplants might help? That sounds right up our street! And got on board. I’m sure they’re always looking for ways to improve the decor of their shuttles.
It is also worth mentioning that this was before the ISS was but a twinkle in the milkman’s eye, BUT around this time some Russian space scientist was testing a sealed environment system that was this whole water purifying, toxic chemical removing, sewage recycling ecological machine.
Nasa needed a quick win! So they tried to solve just the air thing. Baby steps.
What did the study involve?
The study involved putting a load of different houseplants in sealed chambers that were of various sizes but the biggest one was 30 inches x 30 inches x 60.5 inches – conveniently enough, 60.5 inches is a wee bit shorter than my wingspan.
In terms of the size of the plant, the study gives the total plant leaf surface area, so for example the peace lily was 7,960 cm2.
I have no idea how to go about measuring my peace lily but that seems pretty big?
I measured the biggest leaf on my biggest peace lily using a method I found online (width x length x 0.68) and a peace lily with surface area of 7,960 cm2. would be quite a sizeable specimen – one leaf was 171cm2, so this peace lily would have had around 41 big-ass leaves. Perhaps they used several plants.
The plants were also kept at 30 degrees celsius.
The light was 125 foot candles which is…medium verging on bright. An east-facing window on an overcast day.
They then added various nasty toxins: formaldehyde, benzene and trichloroethylene.
What did the study find?
- Plants did remove the toxins pretty effectively in a 24h period!
- The peace lily, for example, removed 79.5% of the Benzene in 24 hours, 23% of the trichloroethylene. Well done. No results for formaldehyde so I assume it did badly.
- Plants removed toxins most effectively when the soil is exposed, so the lowest leaves were removed,
- Plants with the leaves removed also removed a significant amount of toxins.
- ‘Bacterial isolates in the soil are known to degrade toxic chemicals when activated by plant root growth.The plant root-soil zone appears to be the most effective area for removing volatile organic chemicals. So maximise air exposure to the plant, root-soil area.’
Why do I think it’s a scam?
- The plants were kept at 30 degrees celsius which is far hotter than a standard home.
- The very last sentence of the study, before the acknowledgements is VERY important:
‘Activated carbon filters containing fans have the capacity for rapidly filtering large volumes of polluted air and should be considered an integral part of any plan using houseplants for solving indoor air pollution problems.’
- The study also says that results were inconsistent and that other yet unidentified biological factors are also important.
- The summary comes straight from Big Houseplant:
‘Low-light-requiring houseplants, along with activated carbon plant filters, have demonstrated the potential for improving indoor air quality by removing trace organic pollutants from the air in energy-efficient buildings.’
EVEN THOUGH earlier in the paper it says:
‘As temperature and light levels are increased, it is expected that indoor pollution removal rates will increase’.
Ok…then why mention low light if the plants get better at purifying the air when they’re in better light?
WELL
This is a MASTERCLASS in scamming people:
‘It is common knowledge that plants give off trace levels of volatile organic chemicals under certain conditions, so metabolic off-gassing studies were conducted by screening several of the ALCA plants (remember that’s the company making money off this). These low-light-requiring plants were normally maintained at relatively low metabolic rates; therefore one would not expect significant off-gassing of ethylene, terpenes or any other metabolite.
So after all that, what is actually happening is that a healthy plant both absorbs AND RELEASES volatile organic compounds.
If they had left the plants for 48 hours would the levels of VOCs increased again?
- A study aiming to replicate the original 1989 results in 2014 couldn’t get the same results.
- A study done in 2020 found that you would need to put 10-1000 plants per m2 to be more effective at purifying the air than opening a window.
In conclusion:
- Plants do sometimes absorb volatile organic compounds if they’re in a sealed environment, but not always
- Plants also release volatile organic compounds.
- The carbon filter is an integral part of the toxin-removing process. So…an air purifier.
