Journal of the American Society for Horticultural Science 97: 796–800. (1972)
Effect of daylength, light intensity and temperature on growth and flowering in roses.
Roar Moe

Increasing the daylength (from 8 to 16 or 24 h) inhibited budbreak in glasshouse roses, whereas high temperatures (21 or 27 deg compared with 15 deg C) hastened it. The initiation of flowering was promoted by high light intensity and by long days. The effect of daylength was temperature dependent. At low temperatures rose shoots differentiated more leaves before flower initiation with short days than with long days, whereas at high temperatures there was no appreciable difference between daylength responses. The rate of shoot growth was stimulated by long days and high temperatures. The final length of shoots at flowering was considerably greater with 16-h days than with shorter days, but increasing temperature and light intensity both decreased eventual shoot length. The growth of the uppermost internodes, and especially the neck of the flower shoot, was most sensitive to daylength, temperature and light intensity. The number of days from the time of cutting-back until flowering was reduced by increasing daylength, temperature and light intensity.