Do Houseplants Increase Oxygen Levels? - Garden Myths

Do Houseplants Increase Oxygen Levels?
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?
House plants don’t 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.
92 Responses to 'Do Houseplants Increase Oxygen Levels?'
I can’t make the math work regarding 3.7kg of plant biomass created for one day of a person breathing. Humans create 1.15 kg of CO2 per day. C has an atomic mass of 12, oxygen 16. There is greater mass per carbon molecule in CO2 than plant biomass, so less than 1.15kg (my calculations are 0.78 kg) of plant growth would be required for a single day of human breathing.
Plants produce 22L oxygen for every 150g of growth (from ref1). People use 550L of oxygen. For a plant to produce that much oxygen they need to produce 25 times as much growth.
25 x 22 = 550
25 times 150g = 3759g of growth, or 3.75 Kg.
You said that plants produce 22 liters of oxygen for every 150 grams of growth. Does that mean that a plant has no photosynthesis when there is not plant growth? All photosynthesis is associated with the growth process, and a plant at rest has no photosynthesis if it is not growing?
“You said that plants produce 22 liters of oxygen for every 150 grams of growth. Does that mean that a plant has no photosynthesis when there is not plant growth?” – more or less. A plant can go dormant and still have a low level of photosynthesis, but not show any growth.
Example, an ever green is not “growing” much of the year in cold climates, but it does have photosynthesis even in winter.
The way that your citation frames the problem is in terms of all energy going to plant mass, so I do not know how to adjust the formula in your citation.
At a higher level, if one could calculate how much energy is produced from photosynthesis, then 75% of that supports the growth of the plant, and 25% of that supports the metabolism. So you could calculate the amount of energy required for additional mass, and about 1/3rd of that is for energy. But that would not help us calculate energy needs when the plant is not growing.
The point is that plants do produce some oxygen even when they are not growing. Attempting to calculate that for different cases seems to be worth another post.
Not sure what you are referencing, but if you are talking about, “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).” – I would guess that they have already taken the 75% into account.
Regardless of how he made the 150 gram cellulose / 32 gram oxygen estimate, the point is that about 25% of the glucose produced during photosynthesis is for plant maintenance, not growth. So that 25% needs to be added into this article, to properly calculate the amount of oxygen that is being released by the plant, even when it is not growing. I do not know what the precise calculation is. But somehow that calculation needs to be made, and the result should be that plants release more oxygen than they consume during respiration, even when there is no plant growth.
First off, thank you so much for your input Mr. Pavlis, without you I would have never known!
Do you have any insights about Plant specific chemicals ( for example terpenes or other compounds found in plants) on wellbeing?
It may be a stretch but I heard that going for a walk in the woods is good because of the chemicals the trees release. May end up in the same Argument that 2 or 3 plants in a room won´t have the same effect.
I am quite sure 2 or 3 plants do not have the same effect as a forest. Does a forest actually affect us chemically – I am not convinced of that. I suspect it is more about being away from our regular lives.
You Robert are the biggest party pooper I have ever come across. Do your kids ever tell you that you take the fun out of everything? Well I still like your material. Not because of your no-nonsense attitude or pessimistic nature but because of your facts and figures. However, I don’t think you used the correct figures when you said that air has 0.04% co2 and that is the most that houseplants can optimally convert. Outdoor air co2 concentrations sit around 415 ppm meanwhile indoors that number can surpass a thousand.
well, 415 ppm is 0.04% co2 – so it seems you are saying my number is correct.
Even if the inside level is 1,000 ppm, it does not change the level of oxygen produced by plants by any significant amount because of the relative ratio of oxygen to CO2. But if you have a reference to a different calculation, I’d like to see it.
Thank you for your article. I was hoping my few indoor plants could improve the oxygen levels at home now that we have been hunkering down for days with closed windows because of this terrible air quality in Seattle. It’s kind of ironic that as humans we are more concerned in improving the air quality at home than in the wide world… and that makes me wonder about the carbon footprint of growing tropical plants in a temperate climate zone.
Okay, I live in California where currently the air quality is labeled as very unhealthy due to more than 600 fires burning around the state. There are ashes floating in the air outside.
I have 7 kids and have been trying to do anything possible to increase the air quality in our home. There is no outside for them at all…we are getting an air purifier as well.
So, in my particular situation….would adding plant like the Areca Palm, Snake tongue, etc. Help?
The Lung Institute said for one person about 6-8 waist high plants per person would increase the oxygen level. The article was intended for people with COPD.
sorry for the doublepost i just wanted to add that my last post boils down to a 3rd myth 😀 “Do houseplants reduce CO2 Levels?” i think that is the last straw in the question if houseplants improve air. i personally would love to know so i can have a good conscious about whether i need plants in my house or not.
hello, i was wondering about the last part you mentioned. ” 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). ”
that seems logical but 20.95% is the “optimal” amount of O2 in air. lets say you are working in a small office with a lot of people, CO2 levels can rise higher than 0.04%. (there are little CO2 meters that you can buy to keep track of it) so i think people are rather wondering if plants can get the air back to an “optimal” composition instead of raising the O2 levels higher than usual.
I have seen on many documentaries that the planets oxygen level used to be higher (30% during the jurassic period and CO2 levels at 0.12%)this is always attributed to having more plants. Do plants then increase CO2 levels just at a much lower rate than O2? After all they respire all the time but only photosynthesize at night.
It was also said that this contributed to the large size of the fauna and flora around that time which tracks with your explanation on energy production.
So if an increase from 21 to 30 is enough to sustain dinosaurs is an increase from 20.95 to 21 not insignificant after all?
The size the very big animals (dinosaurs, pterosaurs) in the Jurassic Period can only be explained by the Earth having a lower surface gravity than now.
I would like to know why our atmosphere has 9% less oxygen now, where did the extra oxygen go to?
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?
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.
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.
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.
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…?
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!!!
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!
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.
The second study is interesting, but not representative of the average home. You really can’t extrapolate this to a home situation.
The study concludes “Indoor plants could not only decorate the indoor spaces,
release of pressure and tiredness, they could improve the
quality of indoor air condition and reduce the pollutants in the
air. ”
But this study did not look at pollutants at all – so that conclusion can’t be reached by this study.
The conclusion says nothing about a normal home, nor does it tray to extrapolate their findings to a normal home. So your statement “So, houseplants can in fact improve the air in our home” is not correct.
Just to add that plant growth doesn’t necessarily mean the plant is getting bigger. Plant growth also means the plant is, for example, producing new leaves to replace old dead ones. The plant stays the same overall size, but is still producing oxygen.
Everything that Robert Pavlis has stated is very accurate. This is coming from someone with a B.S. in biology and chemistry, M.S. in molecular biology, and has performed academic research on plant metabolism, and an avid grower of indoor plants. Plant respiration is directly tied to their metabolisms and growth rates. Those things occur far more slowly for most indoor plants to have any measurable difference in a house with just 1 human in it. I fancy indoor avocado trees, and they get quite bulky, but I don’t kid myself in thinking that my avocado trees are doing anything significant against the pounds of dust mites in my house eating the ridiculous amounts of dead skin my 6 house members flake off each day (ignoring my 2 cats and Australian red hound). I love plants. They are better than white walls for your psyche. They matter. Life matters. They are not super-powered though. I read a article from an organization promoting the planting of 6-8 trees per person globally because that is the type of balancing required to cancel a person. For air purification don’t be penny-wise pound foolish and believe in falsehoods.
I have four Sansiverias in my bedroom and I feel the difference they made. Because of the smog and low temperature I don’t open windows in winter months. I sleep in a bed with my wife, so two persons lying next to each other produce CO2 for many hours. Plants are close to our heads, so you can say that we are the minority that have they noses right next to them, but I sleep and feel much better since I have them. The level of oxygen in the morning in my bedroom is significantly higher than it used to be and it is a fact you can feel, you don’t need a special equipment to measure it.
Your articles are very simplified. You give numbers about air that every kid learn, but you have forgotten that air is very different around the globe. In very polluted areas its % structure is different and this difference causes cancer in thousands of people every day. You write in English so many people around the world may read your articles and decide not to have plants, which may help them. You are so sure about being right and give opinions what most people do or what most people have (I assume you have travel a lot so you know what are the standards of living around the world) but don’t even notice that you put thousands of species (and milions years of evolution) into one word.
Re:”The level of oxygen in the morning in my bedroom is significantly higher than it used to be”. How did you measure these levels? What were the numbers? I’ll bet you did not measure them and that you really have no idea how they changed.
Re:”In very polluted areas its % structure is different” – do you have some reference to confirm this claim? Even if the values are different in a particular city, it does not change the fact that the amount of oxygen produced by plants will not change the values significantly enough to make a difference.
The composition of air you gave applies if it is fresh. If it is “stuffy”, the scenario of interest, it will be CO2 heavy and plants will have the potential to greatly improve its quality. This article ought to be corrected.
Listen to this podcast segment from The New Yorker Radio Hour. It’s about indoor vertical gardening. They discuss depleting the CO2 in the room enough that the plants were stunted. A fascinating segment overall. http://www.wnyc.org/story/farm-grows-newark-rerun
This is not how gases work in localized, real world events. You are using data for an aggregate O2 and CO2 analysis. In the real world, the immediate area surrounding the plant’s stomata will be rich in O2, significantly so. Lean nto a large, dense, leafy indoor plant, and inhale.
There is no way, logically, that that breath will only contain 0.05% more O2.
One consideration that should be tested: The average atmospheric concentration of CO2 at sea level is about 400ppm, (0.04%) as you state. However, the level inside of a home, office or gym full of sweaty humans, can easily rise above 1000ppm thanks to our own respiration. At 2000ppm you’d have trouble getting a full breath while moving around. At 3000ppm you’d start breathing like a the anonymous creep on the other end of a prank phone call.
This is all to say that while outdoor plants can only hope to convert 400ppm of atmospheric CO2 into O2, indoor plants may have the opportunity to convert far more CO2 because of its greater concentration. The limiting factor is the plants’ growth rate, rather than the amount of CO2 in the air.
I wanted to echo what eacornelius wrote. We have begun to measure the air quality in our office, and the carbon dioxide climbs up really high each day, over 2000 ppm. The average quantity in the outside air is around 500 ppm, so the quantity of carbon is 4 times its normal outdoor rate. During weekends, the rate in the office falls to between 470 and 530 ppm.
At rates over 1000ppm, the air in the office is noticeably stuffy and people are drowsy. In this sort of case, having indoor plants may make a noticeable difference in the air quality when the ventilation is poor.