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
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.
are there any points of house plants? or would getting some potted small to medium size evergreen trees and ferns be pointless in my house?
Buy them to enjoy them, not to create oxygen or clean the air in your home.
What about air purifiers? Do you believe that they may help clean the air in a home? Any favorite ones?
That is not my expertise.
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.
So in regards to oxygen theres no significant benefit. I had heard that they can help in other ways as well, such as humidity, is there any truth to that?
They do add humidity to the air, but again it really depends on how many plants you have. A few houseplants won’t do anything. Go to a tropical greenhouse and the humidity drips off the walls.
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.
The The Lung Institute should know better, but it is a common myth. send them a link to my article.
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.
The main point is that plants in the home have such little effect on oxygen and CO2 levels that they don’t matter.
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?
A small increase might be significant in geological time frames, over the whole planet, but we are talking hours in a home.
Or maybe the amount of nitrogen in the atmosphere has increased since then, and where did it come from?
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?