2020 Volume 89 Issue 1 Pages 61-68
The aim of this study was to develop efficient night cooling technology to produce high-quality carnation cut flowers. The effects of temperature and timing of night cooling treatments (applied using a heat pump) on the flowering time and quality of cut flowers were investigated for standard type carnation flowers grown in a greenhouse in hot conditions. In the first experiment, rooted cuttings of the carnation ‘Exceria’ were planted in a greenhouse on July 6, 2012. Night cooling treatments at 18°C, 21°C, and 24°C were carried out, and the harvested cut flowers were compared with those of a non-cooled control group. For flowers harvested in November, those from plants subjected to the night-cooling treatments had harder stems compared with those of the non-cooled control. In the next experiment, to determine the best timing and duration of the night cooling treatment, we applied three treatments to rooted cuttings planted on June 18, 2013; overnight cooling from sunset to sunrise, cooling for 4 h from sunset (End of Day cooling: EOD-cooling), and cooling for 4 h before sunrise (End of Night cooling: EON-cooling), and compared them with a non-cooled control. For flowers harvested in December, the node order of flowering was the same in the EOD-cooling treatment and the overnight cooling treatment, and was lower than those in the EON-cooling treatment and the non-cooled control. The number of days to flowering was shorter in the EOD-cooling treatment than in the non-cooled control. In October and November in the harvest season when the high temperature influenced the early growth stage, the stem quality of cut flowers was improved by night-cooling treatments, as indicated by a significantly smaller stem weeping angle than that in the non-cooled control group. These results suggested that an EOD-cooling treatment at 21°C for 4 h from sunset was as effective as an overnight cooling treatment to improve the quality of cut flowers by promoting stem hardness and flowering. This method is a cost-effective and efficient thermal management strategy to produce high-quality carnation cut flowers in hot conditions.
