SUPPLEMENTARY LIGHTING OF SELECTED ANNUAL BEDDING PLANTS IN COASTAL WASHINGTON STATE
R.A. Norton
A considerable portion of the land area in northern latitudes is frequently buffeted in the winter months by a series of low pressure systems. The Pacific Northwest of the United States and Northern Europe are two such areas similarly plagued by a dense cloud cover which may reduce winter light levels to below the compensation point for some plants and, from a commercial standpoint, reduce them to an unsalable condition.
In comparison with other parts of the United States, the Pacific Northwest, with its abundant water power has, in addition, the lowest power rates in the country. Thus, there is a great potential for artificial lighting of plants - not only to cause a reproductive response which requires comparatively little light energy, but also to increase the quality of vegetative growth, particularly of ornamental plants.
At present this potential has not been utilized for a number of reasons. In the past, Northwest growers could sell their production without feat of competition from other areas. No longer is this the case. Though a few have experimented on their own with various light sources, they are still groping for one which is distinctly superior for supplementary lighting at a cost which will allow a significant return of their investment in equipment and electrical power. A number of light sources have been advertized and sold, sometimes with disappointing results. Finally, winter light conditions and markets vary from year to year. The grower must spread his costs over the entire year even though supplementary lighting is needed only four to five months for most crops.
The Northwestern Washington Research and Extension Unit of Washington State University became engaged in 1963 in studies, first with CO2, and then with supplementary lighting to develop an economically feasible lighting system for chrysanthemums, bedding plants and perhaps other plants*. These crops, along with lilies and poinsettias are the major glasshouse crops of the area. The latter are produced satisfactorily under available light conditions. Total glasshouse production in Washington State is valued at more than $4.5 million wholesale, annually. This paper will deal only with the research on bedding plants.
The experiments discussed in this paper were conducted in the same glasshouse range, a series of four adjacent units running in a northsouth direction. The individual houses in this range are 25' x 25' with pad and fan ventilation and each contains eight 4' x 10' raised benches.
Norton, R.A. (1971). SUPPLEMENTARY LIGHTING OF SELECTED ANNUAL BEDDING PLANTS IN COASTAL WASHINGTON STATE. Acta Hortic. 22, 131-141