Effect of Daylength, Light Intensity, and Temperature On Growth and Flowering in Roses1

Abstract

Abstract Increasing daylength inhibited budbreak, while high temp hastened it. The initiation of flowering was promoted by high light intensity and long days. The effect of daylength was temp dependent. At low temp rose shoots differentiated more leaves before flower initiation with short days than with long days, while at high temp there was no significant difference. Rate of shoot growth was stimulated by long day and high temp. The final length of shoots at flowering was significantly longer with 16-hr days than shorter days, while increasing temp and light intensity decreased shoot length. Growth of the uppermost internodes, especially the neck, was most sensitive to daylength, temp, and light intensity. The number of days from cut back until flowering was decreased by increasing daylength, temp, and light intensity. The great fluctuation in number of days from cut to cut in greenhouse roses in the course of the year was due to change in light intensity, daylength, and temp.