Winter is a difficult period for houseplants. Many plants don't receive sufficient light because of the short winter days, low angle of the sun, and often overcast weather. While houseplants differ in their lighting requirements, all would benefit from supplemental lighting during the winter months.
Light can be broken down into various wavelengths. Those wavelengths that are perceived as colors are in the visible spectrum. Plants make use of all visible light. Red and blue, however, are the most important for plant growth.
The key to growing healthy houseplants is the light source. Most homes are lit with incandescent bulbs. Unfortunately, they are not a good light source for houseplants. Incandescent bulbs emit light primarily in the red portion of the visible light spectrum. They are also inefficient, 75 to 85 percent of the energy is lost as heat. Foliage which comes into contact with a hot incandescent bulb will be burned.
Fluorescent bulbs are better sources of light for houseplants. Fluorescent tubes give off little heat and produce two and a half to three times more light than incandescent bulbs of the same wattage. They also produce light over a broader range of the visible spectrum, however, blue is predominant. In addition, they are available in square, tubular, and round shapes. Special fluorescent lamps are available in various colors, such as cool and warm whites, daylight, and natural. Warm white fluorescent tubes emit a higher percentage of red light.
"Grow lights" are also available to indoor gardeners. They emit light primarily in the red and blue regions of the light spectrum. However, "grow lights" give off less light than standard fluorescent lights and are quite expensive. A fluorescent unit containing two standard 40 watt fluorescent tubes or one cool white and one warm white tube provides adequate light for house plants and is much more economical.
In well-lit locations, artificial light may be needed only for a few hours in the evening during the fall and winter months. In darker areas, operate the lights for 12 to 16 hours per day. Since light intensity drops rapidly as the distance from the light source increases, houseplants should be placed within a few inches of the lights. Place plants that have a high light requirement directly under the lights and plants that can tolerate lower levels to the side.
This article originally appeared in the October 11, 2002 issue, p. 123.