ROOT ZONE WARMING OF SPRAY CHRYSANTHEMUMS IN HYDROPONICS
Culture in hydroponics advanced mean harvest date by up to 12 days compared with response group time, but there were time of year and cultivar differences. With the exception of the low-temperature sensitive cv. Super Yellow crop timing and yield were satisfactory at the low night temperatures. Harvesting delays were increased as the temperature was lowered. Mean harvest date for the cvs. Flamenco and Hurricane was delayed by 6 and 15 days respectively when grown at 9°C for cutting in late January to early April.
At all air temperatures root zone warming had only a small influence on mean harvest date with maximum reductions of ca. 1.5 days. Elevated root zone temperatures did not compensate for reduced shoot zone temperatures.
Fresh weight of cut stems increased at lower air temperatures and higher solution temperatures, with a consequent improvement in flower quality.
The calculated potential energy saving for the duration of the low night temperature phase varied from 33.6% up to 67.2% depending on time of year and thermostat setting.