The purifying power of a poinsettia

13 years ago

By Doug Saball
    In the late 1980s, a study by NASA resulted in excellent news for homeowners and office workers everywhere. The study concluded that common houseplants not only make indoor spaces more attractive, they also help to purify the air!
    The study tested primarily for three chemicals: formaldehyde, benzene and trichloroethylene. Formaldehyde is used in many building materials including particle board and foam insulations. Additionally, many cleaning products contain this chemical. Benzene is a common solvent found in oils and paints. Trichloroethylene is used in paints, adhesives, inksand varnishes.
    One of the holiday‚Äôs standard house plants are poinsettias. They come in a variety of reds, pinks and whites. But what can be done to make holiday poinsettia turn red again next year?
    After the holidays, you can continue to grow your poinsettia in a bright, sunny location. Once frost danger has passed, you can put the potted plant outdoors in dappled (filtered) light, or leave it in that sunny spot indoors. Water and fertilize it to keep the plant growing actively. Cut it back in early July, trim one-fourth of the growing tips to encourage branching. Leave at least two to three large leaves on each stem. Continue watering and fertilizing.
    If you have kept the poinsettia outdoors, wash it carefully with diluted soapy water before bringing it back into a bright indoor location in early autumn (late August to early September) when nights fall below 60 degrees. Expose the poinsettia to short sunny days and long dark nights to trigger flower formation. Around October 1, cover the poinsettia with a dark plastic trash bag or a box, or put it in a closet so it is completely dark for 12 or 13 hours every night. An example could be; 5 p.m. until 8 a.m. in temperatures around 65 degrees. Uncover it or bring the poinsettia back to its bright location every morning.
    Continue to water the soil when the surface feels dry, and fertilize at half strength about every six weeks. Within six to eight weeks bracts or modified leaves, should begin to turn color again. Continue to give the plant short, sunny days and long, dark nights until the bracts are colored fully. Then put the poinsettia in its bright location permanently.
    After bracts start to color, a long night is not as necessary, but keep giving the poinsettia six to eight hours of bright sunlight until completely colored. Then stop fertilizing and place the plant in its holiday location. Your poinsettia may not be quite as lush or bright as those in the nurseries, but it will still be beautiful. You will also benefit from the air purifying properties of an indoor plant year-round.
    Doug Saball is an environmental specialist with the Maine DEP. In Our Back Yard is an informational column of the Maine Department of Environmental Protection. E-mail your environmental questions to or send them to In Our Back Yard, Maine DEP, 17 State House Station, Augusta, ME 04333.