Dr. Grow: Grow lights can help plants in house

During the months of October, November and December, I often get asked the following question:"I kept my plants outside all summer and they did just fine. I brought them in this fall when it began to get cold. Now my plants don't look good. What am I doing wrong?"

After asking plant owners some questions, I began to realize that there is a common problem. These plants are no longer getting enough light. Let me explain. Plants grown outside during the summer are used to full sunlight. When they are brought inside and placed near a window the amount or intensity of light that they then receive is reduced by up to 50 percent.

This reduction in light intensity is due, in part, to natural cloudiness that we have in the Heartland during the winter. In addition, overhangs on houses reduce light infiltration as do sheer curtains. Even panes of clear glass reduce light infiltration by as much as 10 percent.

The obvious solution to the problem of low-light conditions is to provide your plants with artificial lighting. Don't run out and buy a grow light just yet. There are four concepts that you must keep in mind; light quality, daylength, light intensity and light direction.

To understand light quality, remember back to science class in grade school. The teacher held up a piece of glass called a prism. Sunlight passed through this prism and then shone on a white sheet of paper. The white sunlight was changed into a rainbow of colors ranging from ultraviolet, violet, blue, green, yellow, orange, red and infrared. This rainbow of colors is called the spectrum of the light source.

Plants are obviously used to the spectrum of sunlight. In fact, each physiological function of the plant requires different parts of the sun's spectrum to work. For example, photosythesis, the process of producing sugars and energy by plants, requires two different kinds of red light.

When you go to your local garden center to buy a grow light, ask the clerk to show you the spectrum of the grow light he is selling. Then ask him to compare the grow light's spectrum to that of sunlight. If the spectrums compare favorably, then buy that brand of grow light. If the spectrums don't compare favorably, or if the clerk can't produce the spectrum comparison, then go to another store to make your purchase. Plants can tell the difference between the sun's spectrum and that of a light with a different spectrum.

Plants are used to a specific length of daylight each day. Don't leave a grow light shining on your plants 24 hours a day. Most tropical plants are used to 12 to 14 hours of daylight. Therefore, set your light to turn on each morning at 7 o'clock and have it turn off between 7 and 9 o'clock each evening. Plants need to sleep at night just like we do.

Place your grow light as close to your plants as you can. If you move your grow light from 1 foot from the plant to 2 feet away, the amount of light received by the plant is reduced by three-fourths.

Finally, remember sunlight naturally shines down on plants. It may look aesthetically pleasing to shine a grow light up on a plant, but the plant will not grow very well. God placed most chloroplasts, the organelles that receive sunlight, in the upper surface of most leaves. Very few chloroplasts are on the undersurface of leaves. Therefore, make sure your grow light shines down on your plants.

Selecting and using a grow light for your indoor plants is just a matter of common sense. Keep in mind the concepts of light quality, daylength, light intensity and light direction when you purchase and use a grow light. Your plants will like you for it.

Paul Schnare of Cape Girardeau has been in the lawn and garden business for more than 20 years. He's an adjunct professor in horticulture at Southeast Missouri State University.