By: Deborah L. Brown
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
(Information taken from the NASA report Interior Landscape Plants for Indoor Air Pollution Abatement, September 1989, by Dr. B.C. Wolverton, Anne Johnson, and Keith Bounds, National Aeronautics and Space Administration, John C. Stennis Space Center, Stennis Space Center, MS 39529-6000.)