Houseplants are our often-overlooked helpers in ridding the air of pollutants and toxins, counteracting outgassing and contributing to balanced internal humidity.
Find out which houseplants are our most effective allies in keeping your household air clean and pure.
It is suggested that one plant should be allowed for approximately 10 square yards of floor space, assuming average ceiling heights of 8 to 9 feet. This means that you need two or three plants to contribute to good air quality in the average domestic living room of about 20 to 25 square yards.
Research has shown that these 10 plants are the most effective all-around in counteracting offgassed chemicals and contributing to balanced internal humidity.
- Areca palm
- Reed palm
- Dwarf date palm
- Boston fern
- Janet Craig dracaena
- English ivy
- Australian sword fern
- Peace Lily
- Rubber plant
- Weeping fig
Although many plants like light, they do not all have to be placed near windows. Many indoor plants originated in the dense shade of tropical forests and have a high rate of photosynthesis. These are ideal for the home and can be placed in darker corners. When positioning plants, try to strike a balance between light and ventilation because the effect of plants on indoor air pollution appears to be reduced if they are set in a draft.
Don't miss our great houseplant growing section with self watering planters, high quality potting soil, organic houseplant fertilizers, sprouting bags and more.
In the late 1980s, a study by NASA and the Associated Landscape Contractors of America (ALCA) resulted in excellent news for homeowners and office workers everywhere. The study concluded that common houseplants such as bamboo palms and spider plants not only make indoor spaces more attractive, they also help to purify the air!
The study was conducted by Dr. B.C. Wolverton, Anne Johnson, and Keith Bounds in 1989. While it was originally intended to find ways to purify the air for extended stays in orbiting space stations, the study proved to have implications on Earth as well.
Newer homes and buildings, designed for energy efficiency, are often tightly sealed to avoid energy loss from heating and air conditioning systems. Moreover, synthetic building materials used in modern construction have been found to produce potential pollutants that remain trapped in these unventilated buildings.
The trapped pollutants result in what is often called the Sick Building Syndrome. With our ultra modern homes and offices that are virtually sealed off from the outside environment, this study is just as important now as when it was first published.
While it’s a well known fact that plants convert carbon dioxide into oxygen through photosynthesis, the NASA/ALCA study showed that many houseplants also remove harmful elements such as trichloroethylene, benzene, and formaldehyde from the air.
NASA and ALCA spent two years testing 19 different common houseplants for their ability to remove these common pollutants from the air. Of the 19 plants they studied, 17 are considered true houseplants, and two, gerbera daisies and chrysanthemums, are more commonly used indoors as seasonal decorations.
The advantage that houseplants have over other plants is that they are adapted to tropical areas where they grow beneath dense tropical canopies and must survive in areas of low light. These plants are thus ultra-efficient at capturing light, which also means that they must be very efficient in processing the gasses necessary for photosynthesis. Because of this fact, they have greater potential to absorb other gases, including potentially harmful ones.
In the study NASA and ALCA tested primarily for three chemicals: Formaldehyde, Benzene, and Trichloroethylene. Formaldehyde is used in many building materials including particle board and foam insulations. Additionally, many cleaning products contain this chemical. Benzene is a common solvent found in oils and paints. Trichloroethylene is used in paints, adhesives, inks, and varnishes.
While NASA found that some of the plants were better than others for absorbing these common pollutants, all of the plants had properties that were useful in improving overall indoor air quality.
NASA also noted that some plants are better than others in treating certain chemicals.
For example, English ivy, gerbera daisies, pot mums, peace lily, bamboo palm, and Mother-in-law's Tongue were found to be the best plants for treating air contaminated with Benzene. The peace lily, gerbera daisy, and bamboo palm were very effective in treating Trichloroethylene.
Additionally, NASA found that the bamboo palm, Mother-in-law's tongue, dracaena warneckei, peace lily, dracaena marginata, golden pathos, and green spider plant worked well for filtering Formaldehyde.
After conducting the study, NASA and ALCA came up with a list of the most effective plants for treating indoor air pollution.
The recommended plants can be found below. Note that all the plants in the list are easily available from your local nursery.
1. Philodendron scandens `oxycardium', heartleaf philodendron
2. Philodendron domesticum, elephant ear philodendron
3. Dracaena fragrans `Massangeana', cornstalk dracaena
4. Hedera helix, English ivy
5. Chlorophytum comosum, spider plant
6. Dracaena deremensis `Janet Craig', Janet Craig dracaena
7. Dracaena deremensis `Warneckii', Warneck dracaena
8. Ficus benjamina, weeping fig
9. Epipiremnum aureum, golden pothos
10. Spathiphyllum `Mauna Loa', peace lily
11. Philodendron selloum, selloum philodendron
12. Aglaonema modestum, Chinese evergreen
13. Chamaedorea sefritzii, bamboo or reed palm
14. Sansevieria trifasciata, snake plant
15. Dracaena marginata , red-edged dracaena
For an average home of under 2,000 square feet, the study recommends using at least fifteen samples of a good variety of these common houseplants to help improve air quality. They also recommend that the plants be grown in six inch containers or larger.
Here is a list of resources for more information on this important study:
PDF files of the NASA studies related to plants and air quality:
http://ntrs.nasa.gov/archive/nasa/ssctrs.ssc.nasa.gov/foliage_air/foliage_air.pdf
http://ntrs.nasa.gov/archive/nasa/ssctrs.ssc.nasa.gov/journal_mas/journal_mas.pdf
List of NASA studies related to treating a variety of air and waterborne pollutants with plants:
http://www.ssc.nasa.gov/environmental/docforms/water_research/water_research.html
Our space program has led the way to a fascinating and important discovery about the role of houseplants indoors. NASA has been researching methods of cleansing the atmosphere in future space stations to keep them fit for human habitation over extended periods of time. They've found that many common houseplants and blooming potted plants help fight pollution indoors. They're reportedly able to scrub significant amounts of harmful gases out of the air, through the everyday processes of photosynthesis. Some pollutants are also absorbed and rendered harmless in the soil.
Plant physiologists already knew that plants absorb carbon dioxide and release oxygen as part of the photosynthetic process. Now researchers have found many common houseplants absorb benzene, formaldehyde and trichloroethylene, as well.
Chances are, all houseplants are beneficial in this regard, at least to a certain degree, though they haven't all been tested. Of those tested, not all have proven equally efficient cleaners. Nor can we assume all harmful pollutants can be removed in this manner.
Some houseplants are better at removing formaldehyde from the air, while others do a better job on benzene; none is much help when it comes to tobacco smoke. But there are enough known plants that do a good job of removing pollutants from the air we breathe to cause us to view houseplants as more than just an attractive feature in decorating the interior environment.
These are three of the worst offenders found in relatively new homes and offices. Newer buildings are constructed largely with man-made building materials and furnished with synthetic carpeting, fabrics, laminated counters, plastic coated wallpaper, and other materials known to "off-gas" pollutants into the interior environment.
The advent of the "energy crisis" a number of years back has increased the problems associated with indoor pollutants. Newly constructed buildings are better insulated and sealed tightly to conserve heat or air-conditioning. While it does save both money and energy, this new found efficiency has its downside in that pollutants may be trapped indoors and have less opportunity to dissipate to the outside. The phrase coined to describe this unfortunate result is "sick building syndrome."
If your home is old enough to be leaky and drafty, you may not need to worry about "sick-building syndrome." But if you live in a newer, energy-efficient home with windows and doors tightly sealed, or you work in a building where the air feels stale and circulation seems poor, the liberal use of houseplants seems like an easy way to help make a dent in the problem.
NASA scientists studied nineteen different plant species for two years. Of the specimens studied, only two were primarily flowering plants; chrysanthemums and gerbera daisies. Though commonly used to bring a touch of color indoors, particularly for holidays and special occasions, these plants are generally not kept indoors very long. After they're through blooming they're usually discarded or planted outdoors.
Most of the plants tested are "true" houseplants, kept indoors year-round in our climate, though they may be placed outdoors during warm summer months. One is the common succulent, Aloe vera (now renamed Aloe barbadensis), also known as "medicine plant." Many people already have one in a bright kitchen window because of the soothing, healing properties its viscous inner tissue has on burns, bites and skin irritations.
Most of the plants listed below evolved in tropical or sub-tropical forests, where they received light filtered through the branches of taller trees. Because of this, their leaf composition allows them to photosynthesize efficiently under relatively low light conditions, which in turn allows them to process gasses in the air efficiently.
Soil and roots were also found to play an important role in removing air-borne pollutants. Micro-organisms in the soil become more adept at using trace amounts of these materials as a food source, as they were exposed to them for longer periods of time. Their effectiveness is increased if lower leaves that cover the soil surface are removed, so there is as much soil contact with the air as possible.
Best results were obtained with small fans that pulled air through a charcoal filter in the soil, cleaning more than foliage could alone or in combination with a "passive" pot of soil. Even without the fan and filter, however, houseplants did remove trace pollutants from the air.
The NASA studies generated the recommendation that you use 15 to 18 good-sized houseplants in 6 to 8-inch diameter containers to improve air quality in an average 1,800 square foot house. The more vigorously they grow, the better job they'll do for you.
With the exception of dwarf banana, a fairly unusual plant in this area, the bulk of the list of plants NASA tested reads like a "Who's Who" of the interior plant world. They are:
- Hedera helix English ivy
- Chlorophytum comosum spider plant
- Epipiremnum aureum golden pothos
- Spathiphyllum `Mauna Loa' peace lily
- Aglaonema modestum Chinese evergreen
- Chamaedorea sefritzii bamboo or reed palm
- Sansevieria trifasciata snake plant
- Philodendron scandens `oxycardium' heartleaf philodendron
- Philodendron selloum selloum philodendron
- Philodendron domesticum elephant ear philodendron
- Dracaena marginata red-edged dracaena
- Dracaena fragrans `Massangeana' cornstalk dracaena
- Dracaena deremensis `Janet Craig' Janet Craig dracaena
- Dracaena deremensis `Warneckii' Warneck dracaena
- Ficus benjamina weeping fig
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