The author’s New York office light-case planted with gesneriads, begonias, and other plants
However, before your enthusiasm flies too high, consider this sobering caution. Like anything else, artificial lighting works best only when it is properly planned and executed. Light must have the quality, intensity, and timing that plants need. Specific, accurate, up-to-date information is not always easy to find. Despite many fascinating discoveries and developments, this is still a relatively new horticultural principle, and there is still much more to be learned. Before he begins, the newcomer should locate the very latest and most reliable information; and the experienced grower should keep posted on the constantly changing rules. It has been my pleasant discovery that the big power-and-light companies, ever alert to develop new outlets for their product, are keenly aware of the possibilities of artificial-light plant propagation. Many of them are setting up departments to help horticulturalists. If you are puzzled, try your light company for information. It may take a few phone calls and letters, but eventually I know you will find some likeable chap wanting to help you.
Light shelves of medium height with begonias of many sizes and varieties (note miniatures down front center)
Although it is not necessary to become a botanist, I feel it is urgent to have a clear conception of how plants grow, and particularly how they use light. While we can’t all be electrical engineers, it is also helpful to have some basic facts about electric lights and how they relate to plant growth. But if it were possible, I think I’d consider writing the facts I have with invisible ink. Who knows but what today’s list of rules will be obsolete, and outmoded by new discoveries, before this book can be published?
Botanical Principles
For normal growth and flowering, plants must have light of the proper sort, intensity, and duration. Thus the leaves can perform their function of making starch, then sugar—the mysterious process called photosynthesis. Besides normal growth, plants require an extra supply of sugar and starch for producing flowers. True, plants need light, but they also need dark to convert food into energy and growth. And this means complete dark. It has been shown that if light falls on so much as a single leaf, the entire plant continues to operate as if it were day.
For normal growth and flowers, plants require a certain balance of the red and blue rays of the spectrum. In general terms, blue rays are especially effective in developing leaves, stems, and other vegetative growth, and often in greater proportions for seedlings as compared with mature plants. In general, the red rays keep plant growth sturdy, regulate the development of buds and flowers, affect the germination of seeds and the rooting of cuttings.
For normal growth and flowers, different sorts of plants need light of different intensities—depending usually on available light in their natural habitat. Again in a general sense, light of more intensity is needed for flowering as contrasted with the needs for healthy foliage. But light intensity requirements vary with various types of plants.