Indoor plants have a great reputation for purifying the air in our homes. In Air Purifying Plants – Do They Work?, I debunked the idea that houseplants remove VOCs (toxic chemicals) from our home – it is just a well publicized myth. Several people commenting on that post and the post called A Garden Myth is Born – Plants Don’t Purify Air, to make the point that plants do more than remove chemicals – indoor plants increase oxygen levels in the air. This increased oxygen contributes a lot to our well being – or so people claim. Do houseplants increase oxygen levels in the home?
Plants and Photosynthesis
Through photosynthesis, plants combine CO2 with water and produce sugars and O2 (oxygen). Everyone accepts this fact. In nature, the production of oxygen is so important that without plants we would soon use it up and die.
Logically it follows that plants in a home would also contribute a significant amount of oxygen. There is no doubt that they produce oxygen, but how much do they produce? Is the amount significant compared to the amount we consume? Does a home with plants have a higher oxygen level than one without?
Good Quality Oxygen
A number of websites suggest that plants produce a good quality of oxygen. There is no such thing. Oxygen is oxygen. It is a simple molecule and the oxygen produced by plants is exactly the same as the one found in air.
How Much Oxygen Do Humans Consume?
The science of oxygen use by humans is well understood (ref 1). An adult uses about 550 L of oxygen per day.
How Much Oxygen Does a Plant Produce?
The amount of oxygen that a plant produces is much more difficult to calculate because it depends on many variables. Plants produce oxygen as a byproduct of making sugars, which is their energy source. Slow growing plants need much less sugar than fast growing plants, and therefore produce much less sugar and oxygen.
Low levels of light affect photosynthesis and result in less oxygen production. Temperature, water levels and available nutrients also impact photosynthesis and in turn oxygen levels.
Photosynthesis in a plant results in the plant getting carbon from the air and adding it to its body – leaves, stems and roots. Each molecule of CO2 absorbed, adds one atom of carbon to the weight of the plant and produces one molecule of O2. We can therefore get an estimate of the amount of oxygen produced by weighing the plant.
Marco Thorn has made this estimate and concluded that “for every 150 grams of plant tissue grown, 32 grams of oxygen are released. This is 22 liters of oxygen under normal temperature and pressure” (ref 2).
Plants Also Produce Carbon Dioxide (CO2)
Photosynthesis converts CO2 to O2, but plants also respire. During respiration they convert sugar and oxygen into CO2 and water. This is the reverse of photosynthesis, and it happens in all cells, all of the time, day and night.
Over time plants get bigger and heavier due to the carbon they accumulate. Therefore we know that the amount of CO2 produced from respiration is less than the CO2 used in photosynthesis – or else they could not grow.
Respiration reduces the net amount of oxygen plants produce, especially at night when there is no photosynthesis.
Plants vs Humans
Humans consume 550 L oxygen per day (ref 1). How much plant growth do we need to produce that amount of oxygen?
Plants produce 22 L for every 150 g of growth (ref 2). They would need to increase in weight by 3.75 Kg (8 pounds), each day, to produce the oxygen used by one person.
Keep in mind that plants grow slowly. Adding 3.75 Kg to your houseplants every day would require a huge number of plants.
In most homes the plants cannot produce oxygen at anywhere near the amounts we consume.
Do Indoor Plants Improve the Air?
So houseplants can’t supply all the oxygen we need, but do they increase the oxygen level?
From the NASA Fact Sheet we know that air contains 20.95% O2 and 0.04% CO2. If you had enough plants in a room to use up all of the CO2 and convert it to oxygen, the oxygen levels would increase from 20.95% to 21% (ref 3). This increase is difficult to detect and would have no effect on humans. Keep in mind that this increase is the maximum increase possible and assumes plants would use all the CO2 available. In real life the increase is even less.
Do Houseplants Increase Oxygen Levels?
Not really. They do add oxygen to the room, but in such small amounts that their contribution is negligible. People have a much larger effect on O2 and CO2 levels in a room than plants. If you want to live in a higher oxygen environment – get rid of the spouse and kids!
The main factor contributing to good oxygen levels is the ventilation rate – the exchange of air with the outdoors.
Grow houseplants because you enjoy them – not because they will improve the air in your home.
References:
- How Much Oxygen Do We Inhale; https://www.reference.com/science/much-oxygen-inhale-exhale-b763252ad5727e56
- Oxygen Produced By Houseplants; http://www.madsci.org/posts/archives/1999-02/917906305.Bt.r.html
- Do Houseplants Have an Impact on Oxygen Levels; http://skeptics.stackexchange.com/questions/6066/do-houseplants-have-any-impact-on-oxygen-levels
I know my question is outside the scope of your article, but I thought I would ask. I have saltwater aquariums and it is my understanding that the level of CO2 and Oxygen in the room impact the ph level in the water. Any idea whether plants in the room would have enough of an impact on CO2 and oxygen to impact the ph level of the water in an aquarium?
no impact
I see that holysmoke asked about CAM cycle plants before, but I didn’t see an answer directed at that. I thank you for your no-nonsense posts about houseplant air purification myths, but I have a question on this post. One of the things I read online was that snake plants, using CAM photosynthesis, release oxygen at night and are thus a plant with a noticeable effect in bedrooms. Do you have any more info about how these sorts of plants would affect oxygen levels? My understanding is that they don’t do the respiration that C4 photosynthesis plants do, but I would like some myth-busting done if that’s incorrect.
The point is that humans produce so much more CO2 that plants will not have any significant effect, even with C4 chemistry.
O you are taking all the fun out of my houseplant collection. Now I have no excuse to go buy more houseplants. 🙁
“In most homes the plants cannot produce oxygen at anywhere near the amounts we consume.”
In MOST homes, but not all. You can always go and try to make your house the unique one, where plants make oxygen in sufficient amonuts for everybody.
You would need to live in a greenhouse, not a home.
That is my dream. . . that I could someday LIVE in a greenhouse. Do you see any downside in living in a greenhouse?
I was wondering how humanity ensures enough plants are left growing to ensure that oxygen levels in the air are sufficient, but after reading that 3.75kg of plant material must grow each day to produce the oxygen for each person I realised that the amount of food grown daily for each person or animal must add up to a good proportion of that 3.75kg. In other words, sufficient oxygen production is more-or-less a side-effect of growing sufficient food.
Thanks for the information…
… and sticking around for rebuttals.
Hello Robert,
I think your facts are interesting and mostly valid. Hoever I do have a few disagreements.
1. True that oxygen level don’t increase much, BUT how you define “significant”. When That’s not 0.05% out of 100%, it’s 0.05% on 20.95%.
2. True that mass have to 3.75kg to be good enough. Doesn’t it mean a human also have to loose 3.75kg? Don’t you think plants also need to “go to toilet” same as human?
3. Even if the oxygen level increase “insignificantly”, you can’t conclude that keeping a plant is “insignificant”. You are very mean! Because the cat and dog, wife, and kids would reduce oxygen level and you’d kick them out for goods?
4. I myself sleep in 2 bedrooms with opposite conditions, Both with door and window shut:
A. Master bedroom: larger with large beds, and cloths, no sunlight and plants,
B. Secondary bedroom: smaller with alot of rubber, plastic, and stocks, but has plants & morning sunlight.
Sleeping in A will cause headache, and it smelly. Midnight I have to wake and drink about 2 times, then pee once, cough and running nose. Wake up very tired.
Sleeping in B I won’t have to wake up at all, straight overnight. Feel very freshing and nice dreams. Wake up strong and fresh.
My CONCLUSION: Oxygen is not the only benefit of plants. And science haven’t studied enough. They are much more amazing than the numbers you provided. They are beyond words.
Thank you for reading. I really hope you enjoy your plants.
As I pointed out in the post, that 0.05% is the theoretical maximum if all the CO2 is converted. The real number is much lower.
??”you can’t conclude that keeping a plant is “insignificant”.” – I never made that statement.
“They are much more amazing than the numbers you provided.” – true, but in this post I only discuss oxygen value of plants.
But house plants remove toxins and pollutants from your indoor atmosphere – I read the research from NASA and their conclusions. Unless they are making it up and sending plastic plants to ISS to keep the Astronauts happy…?
You did not read the NASA study. It never measured air in homes, nor did the study make any claims about plants cleaning the air in your home.
https://www.gardenmyths.com/garden-myth-born-plants-dont-purify-air/
On the flip side then, would having many indoor plants in an apartment with some ventilation at night be hazardous to human respiration (and health)?
no
Quasi-related question: how many outdoor plants per person would it take to bring our global CO2 levels down? If everyone grew an extra tree, would that make a difference? I have a small nursery with about 1,500 plants and trees on 3/4 acre, am I helping the neighborhood air quality by much or is it just fanciful thinking? Thanks!!!
Current trees use about 25% of the co2 we produce. We would need significant increases to remove all our produced co2. But each tree does help.
By saying that the Oxygen level can maximally reach 21%, what are trying to say with this? If there is a human breathing in the room, that human will constantly increase the CO2 in the room. Thus decreasing the oxygen level. So the system will constantly be like: air-> human breathing -> more CO2 + air -> photosynthesis-> more oxygen + air -> human breathing. Also, remember to water the plants!
At 21% oxygen – humans breathing in a normal room will not change the amount enough to make a difference.
What he is trying to say is at normal rates of human breathing and typical interactions between everything that makes up our air would bring us to ~20% oxygen and 0.04 carbon dioxide. If we were to add houseplants to the equation, the absolute MOST we could change in that equation would be to have the plants convert the 0.04% CO2 into O2, bringing it up to ~21%. The humans breathing out CO2 was already in the equation before we brought in houseplants to the system.