Flowering Control of Summer-to-autumn Flowering Small-spray-type Chrysanthemum by Light Culture: Selection of Cultivars Compatible with Day-length near Summer Solstice

Flowering control of field-cultivated summer-to-autumn flowering chrysanthemums was established using light culture and selecting appropriate cultivars. In order to make the technique applicable in wider areas, we attempted to stabilize the period from light-off to anthesis. The effects of natural day-length after light-off on flowering were studied. Long days, especially near the summer solstice in the northern part of Japan, inhibited floral development of some cultivars selected in mid-latitude regions. We characterized and selected cultivars suitable for light culture and that flower stably under longer photoperiods. The use of cultivars with a longer critical day-length for flowering could reduce the delay of anthesis.