For normal growth, and flowers, some plants need dark periods of greater duration. This is the principle called photoperiodism. By now a good many plants have been classified as to this requirement, but there are many others whose needs are yet to be determined. Chrysanthemums, poinsettias, and Christmas cactus, for example, will set buds and flowers only when there are more hours of dark and fewer hours of light. These are called long-night plants. Tuberous begonias, and other summer-flowering types, come into flower when nights are of short duration, and are called short-night plants. Those plants that don’t seem to care one way or another are called day-neutral. For the sake of consistency you might even call them night-neutral. It is also thought that there is some relation between the duration of light and dark periods and temperature. Thus it can be seen how much research is yet to be done. A challenge of course, but that is what makes our scientists great.
Electrical Principles
Artificial light is not the same as daylight—it doesn’t have to be. It needs only to supply the right kind of light (blue and red rays) of suitable duration and intensity. Because it is constant, and consistent, the intensity (as measured in foot-candles) does not have to equal the brightness of a sunny day at high noon. Daylight waxes and wanes from dawn to dark every day, and may be very dim on cloudy and rainy days. Artificial light, coming from generators, is not dimmed by clouds or other external conditions. Duration is controlled by a light switch, or a time clock.
Incandescent bulbs are an adequate source of red rays for plants, but give little blue. They get burning hot, are comparatively expensive, and actually are inefficient to operate. Incandescents are also a source of far-red rays that delay flowering on long-night plants and operate in reverse for short-night plants. According to U. S. Department of Agriculture scientists, incandescent light used as a supplement to fluorescent light “improves the growth habits of many kinds of plants, but is seemingly not required by others.”
Until the introduction of the new Gro-Lux tubes in 1961, fluorescent lamps have given light with more blue than red, and in varying proportions according to the types of lamps. Fluorescent tubes do not get burning hot, and they are comparatively inexpensive to operate, and also efficient. In using the older types, those created especially for illumination, it is important to come as close as possible to the proper balance of the red and blue rays needed by plants. For some plants it has been sufficient to use only fluorescent tubes. For some of the other types many growers use 10 per cent of the wattage in incandescent bulbs.
But the new Gro-Lux fluorescent tubes, developed by Sylvania Electric Products, Inc., are especially for plants and not for illumination. They give a lavender-looking light made up of red and blue rays which are carefully balanced to suit plant needs. Growers who have used them report a spectacular improvement in plant appearance, in plant health, in faster rooting of cuttings, and in increased flowering. If demand warrants it, no doubt other electrical manufacturers will introduce their own brands of fluorescent tubes for plants.
Obviously, in growing plants under artificial light there are so many variable elements it is impossible—and extremely unwise—to set down hard-and-fast rules. The types of plants to be grown, whether the installation is primarily decorative or functional, and the possibility of continuing research outdating your work, all should be taken into consideration when any installation is set up and put into operation.
CONSTRUCTION AND INSTALLATION
Again, I must write in general terms. I have neither the knowledge nor the experience to explain the intricacies of wiring, ballasts, circuits, and the like. This technical information is available from your electrical supplier and from equipment manufacturers, and often is on the cartons in which the parts are packed. Our installation was so outrageously large we had to hunt up a friendly contractor for help. He was a sympathetic man who loved plants and was fascinated by the idea of growing them under lights. Also, he was a cautious person, mindful of the fact that our electrical system was about twenty-five years old. And that stamped it as being an antique (as your light-and-power men will tell you). Since our basement floor was likely to be damp at times, heavy waterproof cables with special plugs and outlets were used, and grounded to prevent shocks, etc. Be careful about your electrical system, especially if you are going to go into anything as elaborate as our first enthusiasms. Don’t build a firetrap for yourself. It’s hard on the plants, not to mention the old homestead.
Whether your plants are to be grown in a garden, or in pots on benches, on shelves, or in a greenhouse-like case, the lineal proportions will be determined pretty much by the space that is available in your house, basement, greenhouse, or perhaps, as was in my case, your office. In small decorative planters twenty-five-watt fluorescent tubes (two feet long) are used most frequently. However, it is important to use enough of them, lined up closely to each other, to give a light of sufficient intensity. In fluorescent tubes the light is most intense in the middle and tapers off sharply at the ends. Since short tubes have more end—and less middle—they give off less light. The “shorties” are less efficient, as your plants will tell you.