Do Indoor Plants Turn Harmful At Night? (CO2 Concentration Analyzed)

Do Indoor Plants Turn Harmful At Night? (CO2 Concentration Analyzed)

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It’s well known that during daylight hours chlorophyll in plant tissue converts light energy + water into sugars + oxygen via the process of photosynthesis. The sugars produced help the plant to grow whilst the oxygen is emitted into the atmosphere as a byproduct.

In the absence of light, plants are unable to produce the same level of oxygen yet continue to respire and release carbon dioxide. 

It’s this carbon dioxide production that has many plant lovers looking for assurance it is safe to keep indoor plants in the bedroom, and that no ill effects will be suffered by sleeping next to them. 

Fortunately the concern that indoor plants elevate carbon dioxide to an unhealthy level at night is unfounded. 

A study by Cetin and Sevik (2016), recorded that the concentration of CO2 released by plants at night was between 3.3 – 9.4 times less than the CO2 removed by the same plants during the day. These findings tell us that houseplants which are healthy will always contribute a net daily reduction of carbon dioxide within the room that they are kept in. 

By comparison, the CO2 we ourselves exhale in each breath is 34 mg, which adds up to a rather large 267g being released into our bedrooms across an 8 hour sleep session. 

This amount makes the tiny volume of carbon dioxide released by each houseplant seem almost negligible. 

Whilst the improvement of air quality in the bedroom is certainly one attractive consequence of owning houseplants, there are plenty that make them especially well suited to decorating a home office.

How much CO2 do indoor plants emit at night?

Defining carbon dioxide emissions by an indoor plant at night is challenging as each plant will contain a different surface area of plant tissue over which gaseous exchanges occur. Moreover, different species absorb gases at different rates.

The most difficult characteristic of all to account for is that plants absorb CO2 (photosynthesis) and release it (respiration) simultaneously.

Following the loss of sunlight, absorption of CO2 doesn’t just stop instantaneously, it gradually reduces as photosynthesis slows to a halt, whilst respiration continues in all cells day and night. 

The closest we can come to determining what amount of CO2 indoor plants emit at night is to look at data captured by a controlled study which grew plants in a 0.5m3 sealed space.  

The results demonstrated indoor plants can increase the concentration of carbon dioxide at night by between 84ppm – 351 parts per million. This is heavily outweighed by the reduction of CO2 concentration as a result of photosynthesis during daylight hours.

Plant Increase in CO2 concentration during the day Reduction in CO2 concentration during the day
Rubber plant (Ficus elastica)
Yucca plant (Yucca massengena)
Croton plant (Codiaeum variegatum)

Is it unhealthy to sleep with plants in the bedroom?

It’s perfectly safe to sleep in a room packed full of indoor plants as their presence will always contribute a net reduction in the carbon dioxide concentration within the room in which they are kept

There is no risk that houseplants will cause you to experience negative effects such as headaches, fatigue or loss of concentration that you would normally expect when CO2 levels in the environment exceed 1,000ppm.

In fact, some plants even continue to release oxygen during the hours of darkness when you would normally expect CO2 levels to rise. 

Desert dwelling plants, such as Sansevieria, have evolved to preserve water stores and only open their stomata for gaseous exchange during the night. Oxygen is then expressed into the atmosphere during dark using a particular type of photosynthesis called Crassulacean Acid Metabolism (CAM). 

Moreover, keeping plants in a room where the carbon dioxide concentration is elevated (due to you breathing in and out in the same room for multiple hours during sleep) will actually benefit the plant’s conditioning, which in turn will allow it to work more efficiently at generating oxygen during the day.

So far from being unhealthy, you’ll actually be creating a healthier bedroom by introducing indoor plants to your sleep zone.

Chris Dosser

Chris Dosser

Co-Founder of Eden Indoors

Chris is a self-taught horticulturist with over a decade of experience caring for houseplants and creating lush, thriving indoor oases. He specializes in Monstera, and by self admission has a serious problem with buying and propagating rare indoor plants!

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