November 17, 2003

Houseplants Help Clean Air In Your Home
by James L. Cummins

Many of us like plants for their blooms, but plants also serve a valuable role in cleaning the air. There are many things in our lives, from adhesives to upholstery, from appliances to furniture, that give off toxins. Research shows evidence that houseplants improve air quality. Much of this research has been conducted by former National Aeronautics and Space Administration (NASA) research scientist Bill Wolverton, who first researched plants as part of biological life-support systems for space travel. Wolverton determined that plants absorb airborne pollutants as part of their normal processes. Unlike animals, they take in carbon dioxide and emit oxygen.

Now retired from NASA, Wolverton is promoting houseplants in his book How to Grow Fresh Air and through his business, Wolverton Environmental Services in Picayune, Mississippi. But while other studies have verified and extended his findings, the precise filtering capacity of plants outside the laboratory remains an open question.

While one plant may clean the air in a small, confined space, getting those same results for a whole house would require many more plants. Part of the uncertainty comes from the question of ventilation. In sealed chambers, plants have filtered as much as one-tenth of the air every hour. Wolverton, however says the typical air change in a house is more than 40 percent an hour. And some structures are far more airtight. "Tightly sealed buildings create conditions very similar to static lab tests in that there is very little movement of air," he maintains.

Another concern is the static nature of lab tests, in which a plant processes a limited amount of toxic material. Most indoor air pollutants are continually emitted by their sources. Wolverton counters that in tests he and colleagues have found that a plant can continuously remove formaldehyde from the air. Not only that, he has found over time at least one plant, the lady palm, actually becomes more efficient at disposing of the gas.

Evidence suggests benefits beyond anything demonstrated in the laboratory. "I get calls from people all the time who tell me their headaches or sore throats or other 'sick building' symptoms have either gone away or greatly diminished after they've brought in plants," says Jan Roy, managing director of the Plants for Clean Air Council.

Because each plant has an affinity for different toxins, Roy and Wolverton recommend using a mix of plants. Wolverton has recommended, as a rule of thumb, two to three plants in 8 or 10 inch pots for every 100 square feet of floor space.

Plants should never be thought of a cure-all. "If you have a new building with serious indoor air pollution, even a large number of plants isn't going to solve the problem," he says. But like a cat in your lap, a plant in your "personal breathing zone" - which Wolverton defines as the six to eight cubic feet of air surrounding an individual - can be a comforting presence.

"If you spend a lot of time at a computer or in a chair watching TV, try to have a plant near you," he suggests. "The closer you are to that plant, the more it's going to benefit you."


James L. Cummins is Executive Director of the Mississippi Fish and Wildlife Foundation in Stoneville, Mississippi. Known as "Wildlife Mississippi," the Foundation is a non-profit, conservation organization founded to conserve, restore and enhance fish, wildlife and plant resources throughout Mississippi