Houseplants and clean indoor air

Houseplants are not only pretty; they clean indoor air. You knew, of course, that plants “breathe” in carbon dioxide and breathe out oxygen. As it turns out, houseplants not only absorb carbon dioxide, but also toxic air pollutants. 

The discovery came as a byproduct of space research. NASA scientists needed to find ways to keep the space station habitable by humans. 

They tested 12 houseplants for two years and discovered previously unnoticed characteristics. The plants removed toxic chemicals such as formaldehyde, benzene, ammonia, toluene, xylene, trichloroethylene, and even carbon monoxide from the air.

Since then, other studies have added to the list of houseplants that help purify indoor air. 

Sick building syndrome

In recent decades, houses and other buildings have been sealed in order to minimize the exchange of indoor and outdoor air. That practice has the advantage of eliminating drafts. It cuts the cost of heating and cooling the building. 

Unfortunately, sealed buildings have the unwanted side-effect of trapping airborne toxins indoors. The result has been called sick building syndrome. 

A well-sealed building does not by itself cause sick building syndrome. Most modern buildings use man-made materials for interior decorating. Our paints give off volatile organic compounds (VOCs). So do some our synthetic fabrics, (think furniture upholstery, carpeting, and curtains), adhesives, laminates, plastic-coated wallpaper, etc.

People who live and work in these buildings suffer such problems as headaches, congestion, skin rashes, watery eyes, drowsiness, and other allergy symptoms. 

As it turns out, microorganisms are not among the causes of sick building syndrome. Naturally ventilated buildings don’t cause it, and they have higher levels of microbes than the mechanically ventilated buildings do. 

Indoor air pollution can cause or aggravate unpleasant health conditions. A friend of mine once had to change churches simply because of severe allergic reactions to remodeling. After a while, it became apparent that the VOCs would not dissipate quickly from the building and would continue to make her sick.

Houseplants for air quality

The majority of houseplants cannot be kept outdoors except on warm summer days. They are originally tropical or subtropical. (English ivy is one notable exception.)

In their native habitats, filtered light reaches the forest floor through a canopy of taller trees. So these plants thrive in shade. That’s one of the characteristics that make so many of them prized as houseplants. It also helps them process gasses in the air very efficiently.

Microorganisms in the soil also “eat” airborne chemicals. They do so most efficiently if the lower leaves of the plant do not cover the soil.

Using 15-18 houseplants in pots 6-8″ in diameter will remove trace pollutants from the air. The plants work even more efficiently if there is a charcoal filter in the soil and the plants are near small fans that pull air through the filter.

Some plants “specialize” in removing particular pollutants. That is, some may remove formaldehyde but not benzene. Others may be more effective at removing benzene than formaldehyde. None of the plants tested removes tobacco smoke, but several at least mitigate its effects.

Plants tested and found effective

Here are some plants tested and known to improve indoor air quality effectively:

• English ivy
• Spider plant
• Golden pothos
• Peace lily
• Chinese evergreen
• Various palms, including areca palm, lady palm, dwarf date palm, 
• Snake plant
• Philodendron (heartleaf, selloum, or elephant ear)
• Dracaena (song of India, red-edged, cornstalk, Janet Craig, or Warneck)
• Weeping fig
• Schefflera
• Anthurium
• Massangeana cane
• Various ferns, especially Boston fern
• Orchids (dendrobium and phalaenopsis)
• Chrysanthemum
• Gerbera daisy

Chances are that other common houseplants not listed also clean indoor air. On the other hand, no evidence concludes that just any houseplant will remove pollutants.

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Sources:

20 best air purifying plants / Jeffrey Hollender,  Geoff Davis, and Meika Hollender in Ecolife.
Interior landscape plants for indoor air pollution abatement / BC Wolverton, Anne Johnson, and Keith Bounds (National Aeronautics and Space Administration, September 15, 1989)