Exposure of Rooted Cuttings to Long Days, or Mother Plants to High Temperature, Can Avoid Delayed Flowering of Chrysanthemum morifolium Ramat. ‘Jinba’ for Winter and Spring Cut-flower Production

In order to prevent delayed flowering of Chrysanthemum morifolium ‘Jinba’ during winter and spring cut-flower production, the effects of exposing rooted cuttings to long days (the vegetative growth stage), or mother plants to temperature, on the growth and flowering of plants were investigated. Days to flower budding in plants in short days, propagated from mother plants exposed to ambient low temperature, grown at a constant temperature regime of 20°C or 25°C in long days, were reduced compared with those of plants grown at 10°C or 15°C. Flower budding in rooted cuttings grown at 10°C in long days was delayed compared with 20°C or 25°C treatments when the rooted cuttings were subsequently grown at the same temperature in short days. The increase in leaf number in short days was also reduced with 20°C or 25°C treatment compared with 10°C treatment. In response to treatment with a constant temperature regime of 20/15°C or 20/20°C in long days for 2–8 weeks, days to flower budding in short days was significantly reduced in response to 20/20°C for 4, 6, or 8 weeks than the other treatments; differences among these treatments were not significant. Flower budding of rooted cuttings propagated from mother plants grown at a minimum temperature of 15°C was advanced compared with from mother plants exposed to ambient low temperature. These experiments show that to avoid delayed flowering of ‘Jinba’ for winter and spring production, rooted cuttings, propagated from mother plants exposed to ambient low temperature, must grow at a minimum temperature of 20°C for at least 4 weeks, or rooted cuttings should be taken from mother plants grown at a minimum temperature of 15°C.