Breathe Easier with Houseplants?

A recent study finds that a few well-chosen houseplants can help filter toxins from the air, but some pollution experts remain skeptical

02-01-2008 // Amy Coombs

NEARLY A quarter-century ago, NASA scientists published a series of studies that showed palms, ferns and other common houseplants filter certain indoor pollutants from the air. But before Americans could put a fern in every room, doubters—including the U.S. Environmental Protection Agency (EPA)—began questioning whether plants can really make a difference.

Now a study from researchers at the University of Technology in Sydney, Australia, indicates that some houseplants are, in fact, more than decorative. Plant biologist Margaret C. Burchett and colleagues recently tested the impact of two plants, the peace lily and the dracaena “Janet Craig,” on air quality in 60 different offices. After 18 weeks of measurements, the findings were striking: As few as six small potted plants reduced overall toxin levels by 75 percent.

“The most remarkable finding is that the plants seemed to ramp up their filtration abilities when the air was more toxic,” says Burchett. The study, published in the journal Water, Air and Soil Pollution, found that the houseplants tested were better filters during weeks when pollution levels were high, and performance waned when the air was purer. Overall, offices with plants had cleaner air than those left without the additional splash of green.

“City dwellers spend 90 percent of their time indoors, where the air is sometimes more polluted than outdoor air,” says Burchett. “Potted plants are efficient at cleansing indoor air.” Unlike commercial filters that absorb toxins like a sponge—and ultimately end up in landfills—plants break toxins apart by sucking air into the soil, where microbes degrade toxins into fundamental sources of energy and life.

“Palms and ferns are among the best filters,” says Bill C. Wolverton, one of the original NASA researchers to study houseplants.

Wolverton and his colleagues observed that certain palms, along with dracaena and rubber plants, can remove almost every toxic chemical found in the home.

Still, the notion of houseplants as air filters is not without its critics. “[Plants] are a nice addition to most environments, but I wouldn’t rely on them to be air cleaning machines,” says John Girman, the senior science advisor for the EPA’s Indoor Air Division. “I’m glad to see they are doing studies in office buildings, but it’s unfortunate the ventilation rates weren’t measured.”

Ventilation systems can introduce pollution faster than a plant can remove it, and if clean air is flushed into a room it is hard to determine how much impact a plant really has on the air quality. Other studies have traditionally tested plants in small, sealed test chambers rather than real world settings—a method that also has limitations, say critics.

For Wolverton, the criticism comes as no surprise. “We recognized these limitations a long time ago,” he says. “Plants alone are limited in their ability to remove chemicals from the indoor environment, unless, as the critics suggest, a large amount of plantings are dispersed throughout a building,” he says.

Still, he recommends introducing as many houseplants into a room as possible and making sure that they are well cared for. “Don’t overwater, don’t let water grow stagnant in the tray, and use expanded clay or shell pebbles that don’t support mold,” he says. He also recommends creating a “personal breathing zone” in each room. “You will see better results if potted plants are placed near reading chairs and desks.”

Wolverton acknowledges that a few houseplants won’t solve a big indoor air quality problem. “But two or three plants will make a big difference for the average room,” he says.

California writer Amy Coombs specializes in science-related topics.

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