Do Houseplants Increase Oxygen Levels?

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Robert Pavlis

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.
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.

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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.

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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:

  1. How Much Oxygen Do We Inhale; https://www.reference.com/science/much-oxygen-inhale-exhale-b763252ad5727e56
  2. Oxygen Produced By Houseplants; http://www.madsci.org/posts/archives/1999-02/917906305.Bt.r.html
  3. Do Houseplants Have an Impact on Oxygen Levels; http://skeptics.stackexchange.com/questions/6066/do-houseplants-have-any-impact-on-oxygen-levels

 

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

96 thoughts on “Do Houseplants Increase Oxygen Levels?”

    • The reference you quote was not done in a living space, “The study was conducted in a plant growth chamber that was not in contact with outdoor air and whose internal volume was known.” Unlike a room in a house, the relative number of plants vs available air space was high.

      Reply
  1. 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.

    Reply
    • 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.

      Reply
  2. 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?

    Reply
    • “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.

      Reply
      • From what research I can quickly find, it looks like the carbon from photosynthesis is used to generate glucose. About 25% of the energy generated by photosynthesis goes to maintenance and metabolism, and 75% goes to growth of biomass:
        https://www.khanacademy.org/science/biology/ecology/intro-to-ecosystems/a/energy-flow-primary-productivity#:~:text=Plants%20typically%20capture%20and%20convert,energy%20for%20metabolism%20and%20maintenance.

        That makes sense, since the plant needs to expend energy just to stay alive without growing, and in fact it would expend energy even if it were shrinking in size.

        Based on this idea, I think you need to amend your calculations in this article.

        Reply
          • 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.

      • it is said that 70% of the oxygen we breath comes from ocean plants . elon musk was ask why the plants in the oceans are dying and elon said is because there is too much carbon dioxide in the air saturating the water and killing the ocean plants ! Canada reported a 50% drop in maple syrup last year ! Hawaii reported a 50% drop in sugar cane last year , and so did the country of India have a loss of 50% of all their sugar cane production . two years ago it was reported that all the giant redwood trees that are 3000 years old are now dying from the tops down…. 95% of the kelp forests in the pacific ocean are gone ! all the algae in the north Atlantic ocean is dead ..fish and sea weed are being wash up on beaches around the world lifeless and dead ! 400/1000000 ppm carbon dioxide in the air equals only 0.04% of all the air on the planet as this was a year ago ..all the fossil fuel pollution all the rare gasses all the greenhouse gasses equals less than 1% …now carbon dioxide levels are being reported as low as 0.03% that is not enough to keep plants alive and new reports of oxygen levels are dropping proves this fact ..the damage is being done at the bottom of the oceans out of sight ..is it not way past time we stopped the removal of carbon dioxide from the atmosphere before we are all dead from suffocation ?

        Reply
  3. It is not true that plants convert carbon dioxide into oxygen. In fact the oxygen comes from water molecules, not the CO2. Photosynthesis is a very complex sequence of chemical reactions…

    Reply

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