After last week's column on how strategically planted trees and shrubs can cool your home from the outside, remove air pollutants and reduce energy costs, O'ahu resident Pearl Lee e-mailed to ask about plants that can improve indoor air quality.

Lee, who works at the state Judiciary, mentioned a co-worker who has been undergoing chemotherapy treatments and must carefully watch his health. "Since we deal with the public on a daily basis, I'm looking for an office plant that could ... improve the air in his cubicle," she said.

Plants can't do much to prevent the spread of germs, but they can help control harmful compounds — even some linked to cancer — circulating in offices and other indoor spaces, such as carbon monoxide, benzene, formaldehyde and trichloroethylene.

Vegetation removes pollutants from the air by absorbing gases through tiny pores in the leaf surface.

A two-year study by NASA and the Associated Landscape Contractors of America placed a variety of common house plants in a sealed chamber and injected chemicals. The philodendron, spider plant and golden pothos were the most effective in removing formaldehyde molecules. Flowering plants such as gerbera daisy and potted chrysanthemums did best in removing benzene.

Any plant will do you right, but other good choices for reducing indoor air pollution are areca palm, ficus benjamina, Boston fern, Chinese evergreen, corn plant, croton, date palm, English ivy, dieffenbachia, ponytail palm, prayer plant, rubber plant and dracaena varieties.

The study recommended one medium-sized plant for every 100 square feet of office or home space.

Interior landscape specialist Carolyn Goodin of VSPS (Very Specialized Plant Service) in Kahalu'u said improper watering is the biggest mistake folks make when it comes to indoor plant care. Goodin advised sticking your finger through the puka at the bottom of the pot, and if it feels moist, the plant isn't ready for more water. Plants that need less water tend to do better in an office setting because they also generally require less lighting, Goodin said. She recommends pothos, money tree and sansiveria as easy-care options.

For more information, check out former NASA scientist B.C. Wolverton's book titled "How to Grow Fresh Air: 50 House Plants that Purify Your Home or Office Space." Wolverton also recommends using activated carbon in potted plants so the roots can grow right into the carbon and slowly degrade the absorbed chemicals.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.