Shining like the sun

Quite often, tropical plants that are grown inside houses or offices do not do well. They often survive, but don't thrive. Perhaps one reason for this poor performance is the lack of appropriate light. You can often overcome poor indoor plant growth by placing artificial lights near your plant. If you do use artificial light, there are four things that you need to keep in mind.

Plants have photoreceptors, such as chlorophylls, that absorb light of different wavelengths. This means that if you shine a light on that plant, but the wavelength of the light is different than the wavelength that the photoreceptor absorbs, the light will do very little good for the plant. Plants are attuned to the light of the sun. Therefore if you are going to shine a light on the plant in your home, it must emit the same kinds of light as that of the sun. Look for a grow light at your local garden center. Ask the vendor to show you a comparison of the emitted wavelengths of the grow light as compared to the wavelengths of sunlight. The two should be very similar. If not, then the "grow light" is not really a grow light.

Secondly, your light should be positioned as close as possible to the subject plant without getting it so close that heat from the lamp burns the plant. If you double the distance away from your plant, then only one-fourth of the amount of light will hit the plant.

Plants are also attuned to certain day lengths for optimum growth and changes in growth phase. For example in order for some plants to flower, they must be exposed to minimum dark hours per day. Daylight hours range in the region from a minimum of 10 hours during the winter to a maximum of 16 during the summer. It is best to keep the artificial light burning between 10 and 16 hours.

A grow light should also shine down on a plant. If you dissect a plant leaf, you will find that most of the chloroplasts (photoreceptor structures) are located on the upper surface of leaves. The light may look better from a decorating point of view, but from a biological point of view, light directed upwards toward a plant will find fewer chloroplasts to shine on. Therefore the light will not be very efficient.

Artificial lighting is almost always essential for good plant growth, if plants are placed in the interior of buildings away from the natural sunlight filtering through windows, doors, and atriums. Even plants placed near windows will benefit from artificial light simply because light levels inside buildings are generally much lower than light levels outside. Therefore if you have plants in your home or office, you may want to place a grow light near them in order to encourage faster growth rates.

Send your gardening and landscape questions to Paul Schnare at P.O. Box 699; Cape Girardeau, Mo. 63702-0699 or by e-mail to news@semissourian.com.