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Houseplants Have a Job to Do

By Paula Szilard, Colorado Master Gardener

Gardeners have mixed feelings when fall arrives. There is relief that our hard work is finally over, but there is also a sadness that comes with seeing all that green splendor vanish.

Credit: UC Master Gardeners Napa County

Humans seem to be programmed to live surrounded by green. Research has shown that plants provide many psychological and health benefits. For instance, patients in hospital rooms overlooking green areas improve more rapidly than others. Businesses use indoor plants to enhance productivity.  And, in the winter months in the home, plants may help lift our spirits if we suffer from seasonal affective disorder.

In addition to enhancing the visual appeal of our indoor spaces, houseplants bring the green indoors and may be our best bet to improve indoor air quality. They release oxygen and moisture into our dry environment. They clean our indoor air of pollutants, sometimes referred to as volatile organic compounds or VOCs.  These are airborne compounds given off by paint, copiers and printers, cleaning supplies, textiles, floor coverings, gas stoves, dry cleaned clothing and building materials.

Most of the early research in this field was sponsored by NASA for the space program in the mid-1980s. For longer space missions the agency needed a way to keep the air in a spacecraft clean. No, researchers did not send the plants into space! They created similar conditions on earth, carefully measuring the results.

These results were measured in micrograms of pollutants removed per hour and were nothing short of amazing! Interestingly, the stomates are the organelles responsible for capturing these compounds from the air. Researchers tested for gaseous formaldehyde, the solvents xylene and toluene, ammonia and a few other substances. They found that the plants differed in how much of each pollutant they removed. Areca palms (Dypsis lutescens), dwarf date palms (Phoenix roebelenii) and moth orchids (Phalaenopsis) excelled in removing xylene and toluene while lady palms (Rhapis excelsa), king of hearts (Homalomena wallisii), lilyturf (Liriope Spicata) and Anthurium ‘Lady Jane’ were superior in removing ammonia. Formaldehyde was best removed by Boston fern (Nephrolepis exaltata), followed by florist’s mum, (Chrysanthemum x grandiflorum) gerber daisy (Gerbera jamesonii), dwarf date palm (Phoenix roebelenii) and Dracaena‘Janet Craig’. One of the stars of pollutant removal was the peace lily (Spathophyllum sp.).  It removed phenomenal amounts of acetone (nail polish remover), methyl alcohol, ethyl acetate and benzene!

That’s not all. The plants also produced phytochemicals that suppressed mold spores and bacteria in the air. Researchers found, for instance, that a plant-filled sunroom contained 50-60% fewer molds and bacterial colonies than rooms without plants.

Convinced yet? If yes, what plants do you choose? Pick from a variety of the plants excelling in pollutant removal and then check on growing conditions needed. How much light and water does each need? What kind of planting mix does it thrive in?

Sources of additional information:

Wolverton, B. C. How to Grow Fresh Air. London: Penguin Books, 1997.

(Popular presentation of the NASA research.)

Yang, D. S. et al.  “Screening of Indoor Plants for Volatile Organic Compound Removal.”  HortScience 44(5): 1377-1381. 2009. (Data on 28 common houseplants)

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