Many gardeners say that working the soil and caring for plants are great for relieving stress. Increasingly, researchers tell us that cultivating houseplants also may lower the risk of asthma and allergies and reduce noxious fumes and "sick building syndrome."

This new look at plants was sparked in 1984 when NASA senior research scientist Bill C. Wolverton, an environmental engineer, tested houseplants for their ability to maintain clean air for future habitable lunar bases. Wolverton's experiments, conducted in sealed chambers, found that philodendrons and golden pothos were excellent at controlling formaldehyde, gerbera daisies and chrysanthemums were impressive at purging benzene and potted mums and peace lilies were great at removing trichloroethylene.

"If members of your family suffer frequently from sore throats and stuffy noses, they may be reacting to something more serious than allergies or the common cold," according to the Foliage for Clean Air Council of Davidsonville, Md. "Indoor air-contaminants from seemingly benign sources such as gas stoves, furniture, draperies, insulation and carpets can cause a variety of maladies that include respiratory irritation, dizziness, headaches, skin rashes, nausea and vomiting."

While Wolverton and other researchers have shown that plants can reduce levels of these toxins in the air we breathe, the topic isn't without controversy. The main problem is "how many plants does it take to clean the air in a typical home or office." Many researchers say the amount of plant material necessary to clean up airborne toxins is so great there would be no room for people.

In NASA's controlled lab, one plant per 100 square feet of space helped clean air pollutants and combat "sick building syndrome" brought on by release of toxic compounds in an enclosed space. Research continues in light of Environmental Protection Agency reports that cite indoor air pollution as one of the top five public health threats in America.

Some manmade materials, such as particle board, synthetic fibers and plastics, emit harmful formaldehyde (found in grocery bags, facial tissues, carpet backings and cigarette smoke), trichloroethylene (found in inks and paints), benzene (found in oils, paints and plastics) and volatile organic compounds.

In his book, "How to Grow Fresh Air: Fifty Houseplants That Purify Your Home or Office" (Penguin Books, $15.95), Wolverton writes that his favorite plants are the lady palm, peace lily and "Janet Craig" dracaena "because they're easy to grow, resist insects and work wonders" for a variety of pollutants.

In an expanded study, Wolverton assigned plants a rating from one to 10, based on a plant's ability to remove chemical vapors or indoor air toxins, ease of growth and maintenance, resistance to insect infestation and the rate at which water evaporates from the leaves.

Following are some of Wolverton's top-rated houseplants, with their rating and what they best removed from the air during NASA experiments:

· Areca palm (Chrysalidocarpus lutescens), 8.5, all indoor air toxins.

· Lady palm (Rhapis excelsa), 8.5 all indoor air toxins.

· Bamboo palm (Chamaedorea seifrizii), 8.4, benzene, trichloroethylene and formaldehyde.

· Rubber plant (Ficus robusta), 8.0, formaldehyde.

· Dracaena "Janet Craig" (Dracaena deremensis, "Janet Craig"), 7.8, all indoor air toxins, especially cigarette smoke.

· English ivy (Hedera helix), 7.8, formaldehyde.

· Dwarf date palm (Phoenix roebelenii), 7.8, xylene (found in paints, solvents and adhesives).

· Ficus Alii (Ficus macleilandii "Alii"), 7.7, all indoor air toxins.

· Boston fern (Nephrolepis exaltata "Bostoniensis"), 7.5, formaldehyde.

· Peace lily (Spathiphyllum sp.), 7.5, alcohols, acetone, trichloroethylene, benzene and formaldehyde).

· Corn plant (Dracaena fragrans "Massangeana"), 7.5, all indoor air toxins.

· Golden pothos (Epipremnum pinnatum), 7.5, all indoor air toxins.

· Gerbera daisy (Gerbera jamesonii), 7.3, all indoor toxins.

· Dracaena "Warneckei" (Dracaena deremensis "Warneckei"), 7.3, benzene.

· Dragon tree (Dracaena marginata), 7.0, xylene and trichloroethylene.

· Red emerald philodendron (Philodendron erubescens), 7.0, all indoor air toxins.

Other plants believed to help rid the air of formaldehyde include aloe barbadensis, azalea, Chamaedorea, Chlorophyrum elatum, chrysanthemum, Epipremnum pinnatum, Ficus benjamina, mother-in-law's tongue, poinsettia and spider plant.

Other plants believed to help rid the air of benzene include Aglaonema, Chlorophyrum elatum, chrysanthemum, Epipremnum pinnatum and Hedera helix.

Other plants believed to help rid the air of trichloroethylene include Chamaedorea, Chlorophyrum elatum, chrysanthemum, Epipremnum pinnatum, Ficus benjamina and Hedera helix.

For more information contact EPA Indoor Air Quality Information Clearinghouse, PO Box 37133, Washington, D.C. 20013-7133; (800) 438-4318; or Plants for Clean Air Council, 3458 Godspeed Road, Davidsonville, MD 21035; (410) 956-9036.

Tracey C. Rembert of New York Times Special Features contributed to this report.

Published 8/14/1999