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How pure is the air you breathe? Plants are the lungs of the earth: they produce the oxygen that makes life possible, add precious moisture, and filter toxins. Houseplants can perform these essential functions in your home or office with the same efficiency as a rain forest in our biosphere.
In research designed to create a breathable environment for a NASA lunar habitat, noted scientist Dr. B.C. Wolverton discovered that houseplants are the best filters of common pollutants such as ammonia, formaldehyde, and benzene. Hundreds of these poisonous chemicals can be released by furniture, carpets, and building material, and then trapped by closed ventilation systems, leading to the host of respiratory and allergic reactions now called Sick Building Syndrome.
Dr. Wolverton is recognized as one of the world’s foremost authorities in the use of natural processes for environmental pollution control. He has published more than seventy technical papers and has lectured throughout the world. He has authored three books, “Eco-Friendly Houseplants” (Weidenfeld & Nicolson, 1996); published in the U.S. as “How to Grow Fresh Air,” (Penguin, 1997) and is now in 15 translations.
How do plants remove chemical vapor from the air?
- Plant leaves can absorb certain organic chemicals and destroy these chemicals by a process called “metabolic breakdown.” This was proven by a group of German scientists who labeled formaldehyde with a radioactive carbon 14 tag and followed its absorption and metabolic destruction inside a spider plant. The formaldehyde was metabolized and converted into tissue products such as organic acids, sugars and amino acid.
- When plants transpire water vapor from their leaves, they pull air down around their roots. This supplies their root microbes with oxygen. The root microbes also use other substances in the room air, such as toxic chemicals, as a source of food and energy. Microbes, such as bacteria, can rapidly adapt to a chemical contaminant by producing new colonies that are resistant to the chemical. As a result, they become more effective the longer they are exposed to the chemical.
It is also important to remember that the efficiency of plants or a filtering device decreases as the concentration of chemicals in the air decreases.
Do temperature and humidity influence the ability of plants to remove airborne chemicals and microorganisms?
Yes. The transpiration rates of plants are important in removing both airborne chemicals and microbes. When plants transpire (emit) water vapor from their leaves into the air, they also pull air down to their roots. Any airborne contaminants are also pulled down into the plant root zone. Microbes, living on and around plant roots in an area called the rhizosphere, breakdown and destroy the chemicals. Microbes convert these chemicals into a source of food and energy for the plant and themselves.
Both temperature and humidity influence the transpiration rates of plants. Test results show that plants with high transpiration rates are more effective in removing pollutants from the indoor environment.
How do I determine how many plants I need?
The amount of leaf surface area influences the rate of air purification by plants. Generally, the larger the plant leaf surface area, the higher the transpiration rate and the greater the surface area to absorb airborne chemicals.
The basis for recommending the number of plants per room is based upon the average amount of air pollution found in public buildings that were tested by the U.S. Environmental Protection Agency (EPA). The EPA monitored the indoor air quality in hospitals, nursing homes and office buildings for several years and published their findings.
Data was extracted from this report to produce the following table:
Indoor Air Concentrations of Chemicals Found in Various Buildings
Micrograms Per Liter (µg/l)
| Chemicals | Hospitals | Nursing Homes | Office Buildings |
| Chloroform | — | .004 | .002 |
| Trichloroethylene | .002 | .001 | .005 |
| Benzene | .003 | .003 | .005 |
| Xylene | .013 | .005 | .022 |
| Formaldehyde | .106 | .081 | .173 |
Formaldehyde is the predominant chemical found in the test buildings. If sufficient numbers of plants are added to remove formaldehyde, other chemicals should also be removed.
Plants that Remove Formaldehyde
| Common Name | Botanical Name | Removal Rate*(Micrograms/Hour) |
| Boston fern | Nephrolepis exaltata”Bostoniensis” | 1863 |
| Dwarf date palm | Phoenix roebelenii | 1385 |
| Bamboo palm | Chamaedorea seifrizii | 1350 |
| Janet Craig | Dracaena deremensis”Janet Craig” | 1328 |
| English ivy | Hedera helix | 1120 |
| Weeping fig | Ficus benjamina | 940 |
| Peace lily | Spathiphyllum ”Clevelandii” | 939 |
| Areca palm | Chrysalidocarpus lutescens | 938 |
| Corn plant | Dracaena fragrans”Massangeana” | 938 |
| Lady palm | Rhapis excelsa | 876 |
* Removal rate may vary with plant size and growth medium.
** The figures above are the results of sealed-chamber studies and not “real world” conditions. In a real environment, conditions could vary significantly. Therefore, we recommend that one should at least double the number of plants required based upon this information.
What are negative ions?
Ions are charged particles in the air that are formed when enough energy acts on a molecule, such as water, to eject an electron. The displaced electron attaches itself to a nearby molecule that becomes a negative ion.
In nature, ions are formed in a variety of ways, such as UV light, airflow friction, lighting, falling water and by plants. Plant leaves produce negative ions as they emit water vapors. Therefore, plants that have the highest transpiration rates produce the most negative ions. Waterfalls and tropical forests create copious amounts of negative ions. Synthetic building materials, clothing and furniture coverings remove large numbers of negative ions from the indoor environment. The positive static charge of plastics also consumes large quantities of negative ions. Therefore, the negative ion count in modern buildings is often very low.
Since high levels of negative ions are needed for good health, large numbers of indoor plants can improve our health and feeling of well-being. Our studies have shown that large numbers of indoor plants can reduce the levels of airborne microbes. Although we did not measure negative ion levels, the reduction in mold spores and bacteria in the air surrounding those plants was most likely due to negative ions.
Dr. Lohr from Washington State University also published a paper on how houseplants can reduce human stress and increase productivity. These effects are most likely due to increased negative ion levels in offices. Dr. Lohr published another paper where it was demonstrated that houseplants could reduce the dust levels in a computer room by 20 percent. This reduction was most likely from the production of negative ions.
The positive health effects of negative ions have been known for almost a hundred years. The fact that houseplants produce negative ions is a well-established fact.
Do Houseplants Increase Dust and Mold Spores in Rooms?
No. In fact, foliage plants reduce airborne microbes in the ambient air provided that the soil is not exposed. A two-inch (more or less) layer of gravel or other porous material on top of the soil will prevent mold growth. Studies have shown that plant-filled rooms have 50 to 60 percent less airborne microbes than similar rooms without plants.
Therefore, scientific research demonstrates that interior plants can reduce the levels of airborne microbes and dust in rooms whenever a sufficient number of plants are present. Some allergy physicians continue to recommend that patients remove all plants from their homes. However, there is no scientific basis for this recommendation. In fact, plants should be beneficial to allergy patients provided the plants are grown in a manner to prevent mold growth on the soil surface.
Will houseplants in a bedroom remove the oxygen at night?
No. Do the animals underneath the dense, tropical canopy of the rain forest die at night from lack of oxygen? I don’t think so. It is true that some plants use a small amount of oxygen at night. However, others such as succulent orchids and bromeliads actually add oxygen to the air at night. The Sanseviera (Snake Plant or Mother-In-Law’s Tongue), a common easy to grow plant, also gives off oxygen at night. The only effect one should receive from filling a bedroom with plants is a feeling of breathing healthy indoor air. The only caveat is to make sure the soil’s surface is covered to prevent mold spore growth.
Which houseplants are best for your child’s bedroom?
Some houseplants that are considered safe to have around small children include:
- Areca palm
- Lady palm
- Bamboo palm
- Snake plant
- Swedish ivy
- Spider plant
- Yucca
- Corn plant
- Boston fern
Placing plants in a child’s bedroom that are deemed safe should prove helpful. For example, a lady palm and snake plant, which both thrive in low-light conditions, would be ideal in a child’s bedroom. If plants are grown in hydroculture, it is best to place a screen or some other barrier over the top of the pebbles to prevent children from placing the pebbles in their mouth.
Most houseplants do consume a small amount of oxygen during the night. However, it is an insignificant amount when compared to the overall volume of air in a room. Some plants such as the snake plant, orchid and bromeliad actually produce oxygen at night.
Plants that are harmful to children
Common houseplants that can be harmful to children if they chew on the leaves are golden pothos, English ivy, dieffenbachia, philodendron and syngonium. These are some of the commonly known plants but one should consult a trusted plant grower or medical source if concerned about a particular plant.
A book that we highly recommend, How to Grow Fresh Air: 50 House Plants that Purify Your Home or Office, goes into detail and list specific plant types that help promote fresh air in the home and other closed spaces.
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