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Latrest news on houseplants' ability to clear indoor air.

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    Pretty in Purple: Purple waffle plant
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You may recall the NASA study of the late 1980s that demonstrated how indoor plants could clear volatile organic compounds (VOCs) from the air. Now there's more news on the subject from the University of Georgia.

Here's a link to the original NASA research report, and here's a good explanation of it in layman's terms.

At the time, homes and commercial buildings were being insulated more heavily than ever before, causing those inside to breathe chemicals such as benzene and toluene (which come from newspapers, schoolbooks, electric shavers, portable CD players, liquid waxes and some adhesives, according to a University of Georgia report on new research in this field released earlier this month).

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The NASA research was with 11 common houseplants -- bamboo palm, Chinese evergreen, corn plant, two types of Dracaena deremensis (Janet Craig and Warneckei),  English ivy, Gerbera daisy, peace lily, potted chrysanthemum, snake plant, and weeping fig).

It found that some plants were much better than others at cleaning the indoor air.

The University of Georgia's study, which has taken four years so far and will be continuing, also found tremendous differences in the ability of various species of houseplants to clear VOCs from the air, said Stanley J. Kays, one of the lead researchers, in a phone interview.

More on that in a minute.

But one especially interesting finding was about the air quality in tightly insulated homes versus those (usually older) houses that are more drafty. The NASA study thought that poor air quality was probably confined to newer buildings. But the Georgia study disputes that conclusion.

According to the report on the research: "Before testing the plants, the researchers conducted tests for VOCs in three older, upper middle-class homes in Athens, Ga. Older homes are often more drafty than newer homes, which are built tighter to better insulate them.

“The results really shocked me,” Dr. Kays said. “All three homes had surprisingly high levels of organic compounds in their air. These were older homes. So if the levels are high there, then it’s probably widespread in newer homes.”

Dr. Kays, Bodie Pennisi, and their UGA colleagues have tested 32 species of houseplants so far to determine their ability to remove such VOCs as benzene, toluene, octane, trichloroethylene, and a-pinene from indoor air. (These compounds get into our air, UGA notes, from carpet, paint, people, pets, furniture, home electronic equipment, construction materials, and other sources.)

Some species of houseplants are better at removing one compound than others, but five plants demonstrated superior removal efficiency.

They are: purple waffle plant (Hemigraphis alternata) pictured above, English ivy, Tradescantia pallida (purple heart), asparagus fern (Asparagus densiflorous), and wax plant (Hoya carnosa).

In my experience, asparagus fern is the easiest to grow on that list. Wax plant is probably more suitable for experienced indoor gardeners. English ivy is easy to grow, but highly subject to spider mites indoors unless it's provided with high humidity.

Seven plants were judged to have intermediate removal efficiency -- weeping figPolyscias fruticosa (ming aralia), Fittonia argyroneurasnake plant, Guzmania, Anthurium andreanum (a popular Valentine's plant), and Schefflera elegantissima (false aralia).

Other plants were poor at removing VOCs from the air.  That list includes such popular plants as peperomia, peace lily, philodendron, and prayer plant.

What does all this mean to you? Well, it's difficult for laymen to know what VOCs might be in their air, Dr. Kays points out (and the removal efficiency of each plant for the five compounds hasn't been released yet).

But he recommends that all homes include indoor plants, preferably starting those listed above. (The study suggests one plant per 100 square feet.)

What's next in this ongoing research? Ugly plants,says Dr. Kays.

He's not joking. So far the researchers have concentrated on attractive plants, ones that look good and are relatively easy to grow in homes.

But what if  some odd plant that hasn't ever been considered for indoor growing might be a whiz at cleaning the air? It's certainly a possibility. so they're looking at additional species.

Since this all started with NASA looking for ways to remove chemicals from the air of spacecraft, it would be only fitting for some weird Edward Gorey-style plant to turn out to be the big winner.

(NOTE: To go to the Monitor's main gardening page -- which contains articles and blog posts on many topics -- click here.)

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