by Terry Kramer
SINCE MOST OF US THINK OF house plants as green decorations to enhance the inside of a home, it may seem surprising to learn they are actually living air purifiers that can filter out the dirty air we breathe indoors. In fact, researchers at the National Aeronautics and Space Administration (NASA) have discovered that common house plants are effective at removing indoor pollutants such as carbon monoxide, formaldehyde, benzene and trichloroethylene.
Because of the need to conserve energy by sealing up buildings with weather stripping and doublepane windows, ventilation is often poor and fresh air no longer circulates inside during the winter. According to the Environmental Protection Agency the typical American home contains more than 100 chemicals at concentrations 10 to 40 times greater than outdoor levels.
Modern conveniences like stain-resistant carpets, pressed-wood furniture and wall paper treated to resist mold, exude chemicals such as benzene, formaldehyde and trichloroethylene. Common household items such as grocery bags, room deodorizers, waxed paper, facial tissue, permanent press fabrics, inks, oils, paints, varnishes and adhesives also contribute to indoor air pollution, according to the EPA.
In an effort to conserve energy, yet keep indoor air clean, NASA researcher Bill Wolverton found that many indoor house plants can reduce concentrations of formaldehyde, benzene and trichloroethylene up to 90 percent. These living green machines can also remove other contaminants such as cigarette smoke, carbon monoxide, harmful viruses and bacteria, as well as mold spores.
Botanists have long known that plants cleanse the air through photosynthesis, the process where plants absorb carbon dioxide from the air and release oxygen and water vapor.
In Wolverton's experiments he placed several types of plants in sealed Plexiglas chambers injected with chemicals. He found that plants absorbed much of the chemicals. Wolverton also discovered that beneficial bacteria and soil microbes surrounding plant roots digest contaminants and break them down into forms that plants can feed on and make new tissue.
After testing more than 40 species of plants, Wolverton has discovered that plants have different tastes for chemicals. Spider plants, Boston ferns, philodendrons and pothos prefer formaldehyde. Peace lilies filter out trichloroethylene best. English ivy and chrysanthemums consume benzene.
Most of the plants effective in removing indoor air pollutants are not exotic and are readily available. They include English ivy, aloe vera, ficus benjamina, areca palm, bamboo palm, sansevieria, philodendrons, all of the draceneas, chrysanthemums, bromeliads and orchids. Most plants photosynthesize during the day, but Wolverton found orchids and bromeliads do it at night.
The more indoor plants you have, the cleaner your air will be. But you don't need to turn your home into a jungle. Wolverton figures two to three plants in 8- or 10-inch containers for every 100 square feet can do the job.
Healthy, robust plants in top shape are the most effective in cleansing the air. Keep your green machines well tuned and they will do their job efficiently. Here are a few tips:
THINK LIGHT -- When choosing a particular house plant, consider its light requirements. If you can read a book in a room on a foggy day without the aid of artificial light, there is plenty of natural light to suit most plants. If the room is dim choose medium- to low-light plants like snake plant, pothos, philodendron, Chinese evergreen (aglaonema) cast-iron plant. Create more light in a room by using mirrors, painting walls white or supplementing with gro-lights.
Most house plants do not care for bright direct sunlight, especially from south or west windows. Direct sunlight from a warm window will burn the foliage of most plants. Bright diffused light is best. Most house plants can, however, tolerate light from north and east windows.
KEEP THEM WATERED -- The rule of thumb when watering house plants is to water only when the top inch of soil becomes dry. Give the plants a good soaking, enough so that water pours from drainage holes.
Don't water again until soil surface becomes dry. This watering technique helps to leach fertilizer salts out of the soil. Salt build-up is often responsible for browning leaf tips on many plants, especially palms and spider plants.
Over-watering house plants can cause problems. Not only can you kill the plant, you also invite mold to form on the top of the soil. Worse yet, soggy soil attracts fungus gnats, irritating little flies that feed on moist, decaying potting soil. In high humidity climates such as ours it is best to maintain house plants in a potting soil that is not too heavy with peat moss.
PLANTS NEED TO EAT -- Monthly fertilizing with a high nitrogen plant food will keep plants green and growing. Use a liquid fertilizer like 30-10-10 with iron.
BATHING IS A MUST -- At least once a month give your plants a good hosing down, either outside or in the shower. Be sure to wash the undersides of the leaves as well.
Removing household dust from the foliage allows the plants to "breathe" better. It also helps prevent infestations. Palms especially need their leaves washed regularly to deter spidermite infestation.
DON'T SHINE THEM -- Do not use leaf shines of polishes to brighten up plants. These preparations clog the stomata, or leaf pores. Plants need to breathe in order to photosynthesize. If you keep plants well-fed and bathed they will produce their own natural glow.
NO DRAFTS -- Do not place house plants, especially palms, near drafty doors or windows. Pests like aphids, spider mites and mealy bugs easily blow in with the wind.
INSPECT REGULARLY -- Every other week or so take a look at the undersides of leaves and the growing tips of your plants. Spidermites cause mottling or stippling of leaves. Aphids congregate at the growing tips and undersides of leaves.
If plants begin to develop a stickiness on the leaves suspect either aphids or scale. Remove infected leaves and wash plants with insecticidal soap. If infestations are severe, burn the plant and get a new one!
Terry Kramer is a Bayside free-lance writer and owner of Jacoby Creek Nursery.
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