FARGO, N.D. - It's great when science confirms the wisdom of elders. Mom always said houseplants made a home's atmosphere healthier. A research study by the NASA confirmed houseplants' abilities to remove dangerous air toxins.

I learned much about gardening from Mom, who passed away three years ago at age 94. Houseplants were important to gardeners of her generation, and they instinctively knew the air was healthy with the aromatic mix of humidity, soil and greenery. Plants were part of healthy living.

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NASA conducted research nearly 30 years ago to determine if plants could remove toxic chemicals from indoor air. They were looking for ways to cleanse the atmosphere inside future space stations. The closed-in conditions required ways to purify the air of chemicals given off by the space equipment and structural components. The study was the first of its kind, and is still cited today in literature discussing the health benefits of houseplants.

NASA used sealed test chambers that were injected with chemicals commonly found in interior spaces. Scientists studied dozens of houseplant species to determine which, if any, could reduce toxins in the air.

NASA concluded that houseplants were indeed highly effective at removing harmful substances from indoor atmospheres. They published a list of preferred species, along with specific chemicals that each plant was most efficient at cleansing from the air.

Their study has been criticized by some scientists who feel the laboratory test chambers were not modeled closely enough to a typical house to conclude that the results will be equal for homeowners. Additional research under home conditions would be an interesting complement to NASA's findings.

Since most of us don't live in space stations, what does this mean for us? Our homes contain the same chemicals that NASA needed to eliminate from their structures. These contaminants are present in materials we use every day, and from building materials that "gas out" as they age.

The most common indoor chemicals of concern are: benzene, found in plastics, nylon, dyes and detergents; toluene, used in paints, coatings, dyes, adhesives and fragrances; xylene, in cleaning products, printing ink, rubber and leather; formaldehyde, which is very common and found in plastics, resin, adhesives, furniture, insulation, fabrics, carpeting and many building materials; and trichloroethylene, used in adhesives, cleaners and degreasers.

I wish these chemicals produced colored fog as they "gassed out" so we could see what's in our home's atmosphere. But since they're invisible, and houseplants have been shown to cleanse the air of these chemicals, it sounds wise to have plenty of plants.

The scientists who studied the air-purifying quality of plants suggest one or two plants for every 100 square feet of indoor space. For greatest impact, they recommend at least 10 to 18 houseplants in most homes. The suggestion is based on sizeable plants growing in pots 10 to 12 inches in diameter.

Some houseplant types filter certain chemicals from the air, but not others. Topping the list are plants that cleanse the widest array of indoor pollutants.

Here are the best plants for indoor air purification:

1. Peace lilies ranked highest at cleansing nearly all chemicals floating around in today's home air. These were the most effective plants at removing benzene, formaldehyde, xylene, toluene and trichloroethylene from the atmosphere. Peace lilies are common in both homes and offices and perform well even under low-light conditions. They can be located several feet away from a window.

2. Sanseveria, called snake plant, performed second highest, removing nearly all air contaminants. This was good news because they're not only easy to grow but long-living, with plants commonly reaching ages of 25 to 40 years old. Being a succulent, they are tolerant of occasional neglect.

3. Palms included areca, lady and bamboo types. Avoid soggy soil, and watch for spider mites.

4. Golden pothos, also called devil's ivy, is a rapid-growing vine useful for hanging baskets or anywhere trailing plants are needed.

5. Several types of dracaenas made the list, including marginata, Warnecki and Janet Craig types.

6. English ivy has a classic appearance. Occasionally washing the foliage will reduce its susceptibility to spider mites.

7. Chrysanthemums and gerbera daisies are effective purifiers, but they are difficult to maintain as houseplants, other than enjoying them occasionally as blooming florist gift plants.

8. Spider plant has long been recognized as an air cleanser.

9. Aloe vera is also called medicine plant.

10. Ficus weeping fig becomes tree-like as it grows.

11. Chinese evergreen does well in low light.

12. Philodendron air cleaners include both the vining heartleaf and selloum types.

My wife, Mary, and I are huge fans of houseplants. But after viewing the list of indoor chemicals floating in the air, I'm tempted to purchase them by the truckload.