Effects of Environment on Flower Initiation in Carnation

The main object of the investigation was to attempt the separation of effects of photoperiod and total incident light energy in controlling flower initiation in the glasshouse carnation, variety White Sim.

Low light intensities delayed flower initiation. The delay was associated with reduced rates of growth in terms of dry weight, reduced rates of leaf initiation and increased number of leaves formed below the flower. Short days also delayed flower initiation and increased the number of leaves formed below the flower. Photoperiod, however, had no appreciable effect on growth in terms of dry weight or on rates of leaf initiation, but internode length was greater in long days than in short days. A period of illumination given in the middle of the night was more effective in promoting flower initiation than an equivalent period given to extend the day. Internode length was similar in these treatments. Effects of night temperature were less consistent than those of light intensity or daylength but, under most of the conditions tested, high night temperatures (minimum 65° F. (18° C.)) delayed flower initiation and increased the number of leaves formed below the flower. Low temperature treatment of plants at 40° F. (4.5° C.) for one month promoted subsequent flower initiation and reduced the number of leaves formed below the flower.