You’ve probably read it on the internet: plants purify the air indoors.
And you’ll find air-purifying houseplants for sale in garden centers, plant shops and supermarkets.
But do houseplants really clean the air or is this a clever marketing ploy to push you to buy?
Origin of the story
It seems to have started with a study from NASA: Interior Landscape Plants for Indoor Air Pollution Abatement by Wolverton, B. C., Johnson, Anne, Bounds, Keith (September 15,1989)
NASA wanted to investigate whether plants can help clean the air in a closed system such as a space station where people would stay for a long period.
They already knew about the “sick building syndrome”: in a low-energy building, insulation is increased and the building is made as airtight as possible.
Thus, there is a limited supply of fresh outside air and that leads to a number of symptoms: itching eyes, skin rash, irritation and inflammation of the respiratory tract, headache…
How this test was carried out:
The lineup consisted of Plexiglas boxes of 0.76 x 0.76 x 0.76 cm and larger boxes of 0.76 x 0.76 x 1.53 cm.
The plants were exposed to a single dose of pollutants and the level of pollutants in the box was measured for 24 hours.
What was measured:
In this test, volatile organic compounds (VOC) were measured because these are the most common indoor pollutants: benzene, trichlorethylene and formaldehyde.
Which plants were used:
- Gerbera jamesonii (gerbera)
- Chrysanthemum morifolium (chrysanthemum)
- Hedera helix (ivy)
- Dracaena marginata (dracaena)
- Spatiphyllum “Mauna Loa” (Spathiphyllum)
- Sansevieria laurentii (mother-in-law’s tongue)
- Dracaena deremensis “Warneckei” (dracaena)
- Seifritzii Chamaedorea (bamboo palm)
- Massangeana dracaena (dracaena)
- Deremensis Dracaena “Janet Craig” (dracaena)
- Oriana Musa (banana)
- Oxycardium philodendron (philodendron)
- Domesticum philodendron (philodendron)
- Chlorophytum elatum (spider lily)
- Scindapsus aureus (golden pothos)
- Selloum philodendron (philodendron), now known as Philodendron bipinnatifidum
- Aglaonema modestum (Aglaonema)
- Aloe vera
And this is the list of air-purifying houseplants that you will find on many websites, no matter how good or how bad these plants performed in this test.
Conclusions of this experiment:
The plants themselves seem to have no cleaning effect, it is the micro-organisms in the soil which remove the pollutants.
This was later confirmed in other tests.
These micro-organisms are more effective with time: they seem to adapt and to remove more pollutants after repeated exposure.
In addition, you have to remember that the test was conducted in a small box. You can not just extrapolate this to a larger space.
It was also not determined how many plants per cubic meter you would need in a real living space.
And at last, the pollutants were introduced in a one-time dose in the chamber and then measurements were taken for 24 h. In a room, the pollutants are continuously released into the air.
Other tests have been performed, but usually in a small box and with a limited number of plant species.
All the tests show that the plants themselves do not or hardly have a purifying effect, it is the micro-organisms that live in the earth.
A trial has been conducted in Australia where the air purifying effects of plants was measured in real buildings: The potted-plant microcosm substantially reduces indoor air VOC pollution: I. Office field-study by Ronald A. Wood e.a., February 28, 2006.
The tests were conducted in 3 different buildings: 2 with air-conditioning and 1 with natural ventilation. The experiment was conducted in autumn and winter, and therefore the windows were rarely opened.
The first 2 buildings were located in the city center, the 3rd building was right next to a motorway.
Various volatile organic compounds were measured and then totaled in the results.
- in all tests the concentration of pollutants was higher indoors than outdoors, no matter if there where plants in the offices or not
- the air purifying effect grew with time: as the micro-organisms are exposed longer to the pollutants, they remove more pollutants
- the plants had only a significant purification effect when the concentration of pollutants was higher than 100 ppm (parts per million). At lower concentrations, there was no effect.
- no minimum number of plants needed was determined, 3 large plants in a pot of 9-10 liters or 6 small plants in a pot of 3 liters had about the same effect
Do houseplants purify the air in a room: no, the microorganisms that live in the soil purify the air.
The types of micro-organisms do vary depending on the plant species and may be more or less effective with various pollutants.
However, the air purifying effect is only noticeable when the concentration is higher than 100 ppm. Below that concentration, the effect is almost nonexistent.
Does it make sense to buy a house plant to purify the air in your home?
The test which was carried out in real buildings showed that the concentration of contaminants indoors always remained higher than outdoors, regardless of whether or not there were plants.
If you want to clean the air in your home, open the window to ventilate. That will always be more effective, even in urban areas.
Air purifying plants have sense only in a closed building such as an office building or an energy-efficient home, where the windows can not be opened. And then only when the concentration of pollutants is higher than 100 ppm.