Effects of Duration of Exposure to Low Temperatures on Bolting and Flowering of Rosetted Seedlings and Lateral Bud Emergence after Flower Harvest in Elatum Hybrids of Delphinium

Abstract

This study was conducted to determine the duration of exposure to low temperature required to induce bolting of rosetted seedlings and subsequent emergence of lateral buds in Elatum hybrids of Delphinium. When seedlings of 'Blue Springs', which rosettes from autumn to winter, were exposed to natural low temperature until December 5 or 15, plants bolted earlier under long days after being transferred to the greenhouse kept above 10°C than those under natural day length. This result means that exposure to low night temperature below 7°C for 30 days was required to induce bolting of rosetted seedlings, whereas the long day treatment after heating hastened flowering. Lateral buds on the base of main stems were induced to elongate and bolt when plants were exposed to 5°C at night for 30 days after cutting back the main stems in 'Blue Springs' and 'Magic Fountains Sky Blue'. When they were grown above 10°C, they produced 2.1-2.2 inflorescences/plant which flowered 70-74 days after heating. Lateral buds on the base of secondary shoots emerged without rosetting after secondary flowers were harvested in early April and flowered about 2 months later.