Let it grow

By Paul Schnare

Over the past few weeks, several gardeners told me they are moving plants indoors, or they are going to start bedding plants from seed after the holidays. The common question from both groups is what kind of light requirements must be met. "Can I use regular incandescent or fluorescent bulbs as a light source?"

The short answer to the question is no. You shouldn't use either kind of light bulb as a growing light source for plants. You should use a "grow light." A grow light is designed to mimic the same light quality as our sun. Let me explain.

The sun produces light wavelengths from ultraviolet (very short wavelengths) to infrared (very long wavelengths). Different wavelengths affect different chemical reactions in plants.

The most studied and most important reaction in plants is photosynthesis. This series of chemical reactions convert CO2 (very abundant in our atmosphere) to C (carbon) and O2 (oxygen). Carbon is a major building block of all organisms (plants and animals). And O2, of course, is what animals and humans need to breathe in order to stay alive and function.

Orchids sit underneath a Hydrofarm grow light at Sunny Hill Gardens & Florist Wednesday in Cape Girardeau.ANDREW J. WHITAKER

Therefore, if you are going to provide a light source for plants you grow inside your home, you want one that mimics the production of wavelengths as close to that of the sun as possible. This is what grow lights do.

Light intensity also is important. Suppose you place your grow light 1 foot away from the plants you are cultivating. Now if you move the grow light to 2 feet away from the plant, you would probably think the light intensity is reduced down to half of that at 1 foot away. Actually it is reduced to one-fourth of the light intensity that it produced at 1 foot away from the plant. Therefore, it is important to keep your grow light as close as possible to the plants you are cultivating so they will get the highest light intensity possible.

Another concern when using a grow light is photoperiod. This is the length of time the light (or sun) actually shines on the plant you are growing each day. Think of it this way: During the summer we have sun that shines from 5 a.m. to perhaps 8 p.m. This is a long photoperiod. During the winter, the sun may shine only from 6 a.m. to 5 p.m. This is a short photoperiod.

In the Heartland, plants grow rapidly during the summer, but hardly grow at all during the winter. This is partly due to ambient temperatures, but it also is due to the fact that there is a long photoperiod during the summer.

Hopefully with these concepts in mind you can illuminate your indoor plants with a grow light that is placed properly and kept on for the right period of time during the day to keep the plants growing well.