There are plants that improve the indoor climate. This statement is widespread on the Internet. A NASA study that came to this conclusion serves as evidence. However, what is not mentioned in this context is under what conditions and with what objectives the study was carried out.
To what extent can plants improve the indoor climate?
Plants can improve the indoor climate to a limited extent by removing VOCs (volatile organic compounds) from the air. However, regular ventilation is more effective for improving the air than putting up houseplants.
The “NASA Clean Air Study”
The starting point for the much-publicized “NASA Clean Air Study” from 1989 was the question of how the air could be cleaned in closed environments such as in a space station. The researchers were not concerned with the well-known phenomenon of photosynthesis, but primarily with the removal of volatile organic compounds (VOCs) from the air. On the VOC side, benzene, formaldehyde and trichloroethylene were tested; on the houseplant side, 12 different potted plants took part in the experiment. What was measured was whether the concentration of organic pollutants in a closed (sealed) room was reduced due to the presence of the plant.
The results were positive. This subsequently led to the tested potted plants being listed as air-purifying plants. No one was interested anymore in the fact that the experiment was carried out under laboratory conditions.
Review of studies on air purification by plants by Waring and Cummings
The two US researchers Michael Waring and Bryan Cummings did not carry out their own series of tests with plants to improve air quality, but rather analyzed and evaluated the results of a dozen studies from 30 years of research (review). The results for 2019 were published:
- Potted plants can remove VOCs from the air
- in small, sealed rooms
- Time period is between many hours or days
Transferring air purification through houseplants to conventional indoor and office spaces is possible, but not particularly sensible, because effective air purification requires
- 10 to 1,000 plants per square meter of floor space,
- to achieve the same removal rate within an hour as with conventional air exchange.
In other words: Regular ventilation is far more effective for improving the air than putting up houseplants.
Plants in the bedroom
In addition to the NASA study on air purification, there is also a lively discussion on the Internet about plants in the bedroom. While some people literally praise bedroom plants, others warn against their green roommates. The pivotal point of the discussion is, on the one hand, photosynthesis, in which oxygen is released as a waste product, and, on the other hand, the oxygen consumption of plants.
Photosynthesis and oxygen
Bedroom plants have - as can be read on many websites - a special property: They can also carry out photosynthesis at night and therefore release oxygen into the air at night. This is a nice claim, but it has no basis. Because light is necessary for photosynthesis (from “phos” for “light”).
Plants as oxygen competitors
Plants, like all living things, need oxygen to live. However, since they release oxygen into the air, this fact is often neglected during the day. However, when it comes to the night, oxygen consumption suddenly becomes very important. Since houseplants do not release oxygen at night, they become competitors for oxygen in the bedroom. This is also a nice consideration. However, so far there are no known cases in which bedroom plants have become murderers by depriving sleeping people of oxygen. This is because their oxygen consumption is far too low for this.
