The effects of root-zone warming on the yield and quality of roses grown in a hydroponic system

Rose cvs Ilona, Mercedes and Sonia, budded onto R. multiflora rootstock, were grown using the nutrient film technique. A root-zone temperature of 25°C was compared with ambient root temperatures at three night-time air temperatures of 18°, 12° and ambient (9°C), and in two other experiments at 18°, 14° and 10°C. Bloom yield and stem length and diameter were recorded for a 22-week winter/spring period and for shorter periods in the following summer. In Experiment 1 Sonia responded to root zone warming (RZW) by giving 44% more blooms and a 26% increase in stem length compared with ambient root temperature. Ilona gave a yield response only at a night temperature of 12°C, but RZW resulted in 22% longer stems. Mercedes gave 22% more blooms from RZW. Plants from Experiment 1 were used for a second year in Experiment 2. Mercedes produced 113% more blooms from RZW, Sonia 61% and Ilona 42%. Stem lengths were all increased by 6-7%. Experiment 3 used first-year plants. The pattern of yield response to RZW was similar to the other experiments. Mercedes gave 61%, Sonia 24% and Ilona 18% more blooms. Ilona showed the largest increase in stem length (24%). RZW increased the amplitude of the growth flushes, but their frequency was unaffected. Yields during the subsequent summer, when temperature differences between RZW and ambient temperatures were small, indicated residual effects of the winter treatments. Sonia (Experiment 1), and Mercedes and Sonia (Experiment 2) gave significantly higher yields from the RZW treatments. There was no evidence for a decrease in yield caused by RZW, only Ilona in Experiment 3 giving a lower yield in the summer.