An experiment to determine a model for predicting flower size and other characteristics of the rose variety Rosa x hybrida ‘Kardinal’ in relation to greenhouse conditions showed temperature to be the one of the primary factors. The number of days from bud break (BB) to flowering increased from 21.6 to 63.0 days as temperature decreased from 30°C to 15°C. The number of days to flower was primarily influenced by the temperature after the visible bud (VB). This suggests that the temperature before VB may not significantly affect the rate of flower development. Leaf area, stem length and stem diameter generally increased with decreasing temperature, but the best quality of stems was observed at 18°C. Flower dry weight, however, increased from 0.7 to 3.0 g as temperature decreased from 30°Cto 15°C. When plants were moved to lower temperature at VB stage, flower dry weight increased. In another experiment it was found that the optimal temperature for young leaflet growth was 25°C while that of young buds was below 15°C. ISHS Acta Horticulturae 547: III International Symposium on Rose Research and Cultivation and 543 VII International Symposium on Postharvest Physiology of Ornamental Plants. www.actahort.org