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Clean Indoor Air
Back in the 1970s, houseplants were everywhere. Then decorating went high-tech and houseplants lost their cachet. But it turns out there are some very good reasons for growing plants indoors, and you might want to bring some into your 20th-century home.
Houseplants are beneficial in a number of ways. There are aesthetic benefits, of course houseplants add color and soften the architecture of a room. Decades of research have shown that working with plants has psychological benefits, too. The field of horticulture therapy in which psychiatric and rehabilitation patients, nursing-home residents, and prisoners garden and work in greenhouses has developed around this idea. Some plants have healing qualities. Consider aloe, whose leaves contain a sap that soothes minor burns and skin abrasions; or peppermint, which can be brewed into a tea that calms an upset stomach.
But perhaps the most exciting thing houseplants can do for us today is purify the air in our homes and offices. Plants improve air quality simply by absorbing carbon dioxide and increasing oxygen levels in a room. But they have also been found to absorb pollutants from the air inside buildings.
Most people don't think much about the air they breathe at home or at work. We often take for granted that the air we inhale is safe, cooled and cleaned by air conditioners, heating systems and filters. But you might be surprised to learn that the U.S. Environmental Protection Agency now considers indoor air pollution to be one of the top five threats to human health.
Indoor air pollution became a pressing problem in the 1970s, when the energy crisis stimulated development of energy-efficient building techniques and materials. We insulated our homes, energy-stripped doors, and hung double-pane windows in an effort to reduce fuel consumption and energy costs. The energy-saving measures worked, perhaps too well.
The EPA has done numerous studies over the past 25 years that demonstrate measurable indoor levels of more than 100 different volatile organic compounds (VOCs) that are known or suspected carcinogens. When enough of these compounds are present, people working or living in buildings can become ill, developing such symptoms as headaches, allergies, nervousness, loss of appetite, and eye and skin irritations. VOCs are also believed to contribute to the rise in asthma cases, especially among children. In the worst cases, these buildings are called "sick buildings,
because a significant number of people in them develop symptoms.
Modern building materials, furnishings and office equipment contain chemical compounds that escape into the air and accumulate over time. The best way to get rid of VOCs is to ventilate the building open the windows. But even if you can ventilate them, more are continually produced. Using all-natural building and furnishing materials, even if you can find them in this age of dwindling forest reserves, can be prohibitively expensive.
Here's where houseplants come in. About 20 years ago, NASA researchers working on ways to maintain clean air in spacecraft during extended missions discovered that plants are effective air cleaners. A team of NASA researchers led by Dr. Bill Wolverton tested the effects of a variety of houseplants on three air pollutants known to be present in spacecraft. These same VOCs benzene, formaldehyde and trichloroethylene are also present in many homes and offices.
The researchers found that when plants were placed in sealed Plexiglas chambers and chemicals were pumped in, the plants removed up to 87 percent of air pollutants in 24 hours. The plants absorbed the chemicals through their leaves and moved them to the root system, where microbes broke them down. Basically, the plants used the pollutants for food.
The research is still considered controversial. The experiment was performed under controlled conditions, but in a real situation, chemicals are emitted continuously into the air and the environment is not sealed. People enter and leave the building, and conditions change. The EPA says that it might take lots of plants even hundreds of them to clean the air in a typical building. But Wolverton believes only a few plants per hundred cubic feet of space would do the job. Large numbers of plants in a home or office building would raise the humidity level so much that new problems could be created. Molds and bacteria could grow, causing their own ailments in sensitive people. Furniture could warp from the constant dampness. The EPA recommends ventilation and removal of the materials emitting the chemicals as the best way to get rid of the pollution. But it seems that houseplants may indeed be effective remedies for indoor air pollution. Surely it wouldn't hurt to have some in your home.
Higher humidity indoors as long as it doesn't get too high can be decidedly beneficial, especially in winter, when central heating turns our homes into miniature deserts. Dry air dries out the membranes in our noses, which leads to more colds and allergies, and an increased incidence of asthma. Providing good air circulation by not cramming large numbers of plants close together, and allowing the soil in pots to dry out somewhat between waterings should keep humidity from reaching harmful levels.
Which Plants Work Best?
In addition to the plants in the table, other good air cleaners include Boston fern (Nephrolepis exaltata, Bostoniensis), parlor palm (Chamaedorea elegans), areca palm (Chrysalidocarpus lutescens), rubber plant (Ficus elastica), striped dracaena (Dracaena deremensis, Warneckii), and gerber daisy (Gerbera jamesonii). They're all readily available at florists, nurseries and other places where houseplants are sold.
Keep Your Houseplants Happy
The secret to success with houseplants is simple: Choose plants that are suited to the growing conditions available in your home, and they will thrive with a little basic care. Heres a quick guide to the conditions you need to consider.
Light A south window provides the brightest light, receiving sun for much of the day if the window is not obstructed by nearby trees or buildings. South-facing window sills can get quite warm, especially on summer afternoons, but placing a sheer curtain in the window will soften the glare and reduce heat for sensitive plants. A south window affords you the greatest choice of plants, both foliage and flowering.
An east window will be sunny in the morning and will accommodate a wide variety of plants. West-facing windows receive afternoon sun. Because ambient temperatures tend to be warmer in the afternoon than in the morning, plants in west windows must be able to take the heat.
A north window won't get much, if any, direct sun, but if it is clear of obstructions, it can still be bright enough for ferns and a variety of other foliage plants. In winter, a north window sill will be noticeably cooler than a window facing south.
If you don't have much natural light for plants, don't despair. Electric lights can work just fine. Fluorescent fixtures are better than incandescent bulbs, which throw a lot of heat. Use a combination of cool-white and warm-white tubes or bulbs, or use full-spectrum lamps, to supply all the wavelengths plants need to thrive. It's important to position the plants so their tops are just a few inches below the lamps. Leave the lights on 12 to 16 hours a day to supply all the light plants need.
Potting Mixes A loose, light potting mix ensures that roots will get plenty of air and excess water will drain away easily. When soil is soggy all the time, plant roots are unable to take in oxygen and the plant eventually suffocates. Peat-based potting mixes are lightweight and easy to use, but if you are concerned about depleting the world's finite supplies of peat, grow your plants in a medium that contains no peat.
There are lots of good packaged potting mixes on the market. Some contain fertilizers and others do not. Although the fertilizer-containing mixes are convenient, doing your own fertilizing allows you better control. You can, for instance, stop feeding plants when they go into a rest period. If you use a packaged potting mix, make sure it is a potting mix and not just potting soil, which by itself is too heavy and dense for most plants. Look at the ingredients on the bag if you're in doubt.
It's also easy to make your own potting mix. See our recipes below.
Most plants like to be repotted into fresh soil every year or so. For big plants that would be difficult to repot, scrape the top couple of inches of soil out of the pot and replace it with fresh potting mix.
Watering and Fertilizing More houseplants die from overwatering than any other cause. Many plants like the soil to be evenly moist, which does not mean constantly soggy. A good rule of thumb to follow is to poke a finger into the soil; when it feels dry an inch below the surface, it's time to water. Water thoroughly, so excess collects in the saucer under the pot. Pour off any water remaining in the saucer after 15 minutes.
It's important to fertilize houseplants, too, since they will use up the nutrients in the small volume of soil in the pot. Soilless mixes contain no nutrients at all, and plants potted this way will be entirely dependent on you to supply food. Mild liquid fertilizers are easiest to use. Choose a balanced, all-purpose product or, if you garden organically, feed your plants with a seaweed/fish fertilizer or compost tea. Follow package directions for amount and frequency of use or, if you prefer, use a half- or quarter-strength dilution every time you water the plants.
It's most important to fertilize when plants are growing actively producing new leaves and shoots and when flowering plants are setting buds. Following these guidelines will keep your houseplants healthy while they freshen the air in your home.
How to Grow Fresh Air: 50 Houseplants That Purify Your Home or Office, by B.C. Wolverton (Penguin USA, 1997)
Easy-Care Guide to Houseplants, by Jack Kramer (Creative Homeowner, 1999)
Anne Halpin is a freelance writer based in Hampton Bay, New York.