Pollution has long been a concern, but few of us realize that the indoor environment is up to 10 times more polluted than the outdoor one. The Environmental Protection Agency calls indoor air pollution one of the top five public health threats, writes B.C. Wolverton in How to Grow Fresh Air (Penguin, 1996). Today's hermetically sealed buildings, energy-efficient but poorly ventilated and stuffed with synthetic furnishings, contribute to allergies, asthma, and chemical sensitivities. And we're no help; our bodies emit such unsavory "bioeffluents" as acetone and ethyl and methyl alcohol.
The good news is that ordinary houseplants are excellent pollution fighters. When their stomata open to absorb and release air and water, the air moves. This allows the plants to capture toxins, which go into the root systems, where microbes break them down. Saturation and re-release of toxins is not a problem; the removal rate actually improves with exposure. Plants also emit phytochemicals that suppress mold spores and bacteria.
All this from a Boston fern? You bet. Following NASA's lead a decade ago, researchers have determined which plants excel at which cleanup activities. This fern, followed closely by the florist's mum and the gerbera daisy, is tops at removing the most common toxin, formaldehyde, found in everything from facial tissues and carpets to gas stoves and plywood.
The lady palm is the ammonia-removal star; the peace lily best digests human bioeffluents. The moth orchid and dwarf date palm remove the xylene and toluene emitted by ceiling tiles, caulk, paint, floor coverings, and computer screens. But they are not as effective as the areca palm, which Wolverton also considers the most ecofriendly of the 50 house and office plants he describes.
He uses four criteria to rate the plants: removal of chemical vapors, ease of growth and maintenance, pest resistance, and transpiration rate (which means, for example, that one liter of water evaporates from the areca palm every 24 hours). His top 10, in order: areca, lady, and bamboo palms; rubber plant; dracaena "Janet Craig"; English ivy; dwarf date palm; Ficus alii (a new, less finicky fig); Boston fern; peace lily.
Wolverton suggests grouping plants to maximize their efficiency and attending to details such as how much humidity they supply (the proper amount promotes health) and whether they release oxygen during the day (most do) or night (try succulents or orchids in your bedroom). And it's not hard, he claims, to help these natural purifiers thrive.