Effects of Temperature, Photoperiod and Exogenous Gibberellin on Flowering of Clematis terniflora DC.

Vegetative growth and flowering of Clematis terniflora DC. were favored by day/night temperatures of 24°/19°C and 30°/25°C under natural photoperiods of above 14-hr daylight from May through July. However, at 17°/12°C, the shoot growth was significantly delayed and no flower buds were differentiated.Even though plants were grown under favorable temperatures, shoot tips became necrotic when grown under an 8-hr day for one month during May or July. Flower buds were differentiated under natural photoperiods and 16-hr photoperiod, but not under 8-hr or 12-hr photoperiods. Buds require about one month under long days for flower induction to take place provided the shoot reached a minimum critical size which also requires about a month after budbreak. After differentiation occurred, continued exposure of plants to 16-hr days delayed flower bud development, bud break, and bloom dates compared to plants transferred to 8-hr days.Under natural photoperiods, sprays of 100 and 1, 000 ppm GA hastened both vegetative growth and flowering but decreased the number of flowers as compared to the non-sprayed control plants. Eight applications of GA at 15-day intervals compared to one spray treatment decreased the number of flowers markedly and more than half of the flowers produced were abnormal ones with degenerated anthers and undeveloped pistils. Moreover, among normal and abnormal flowers, there were found some flowers with more than 4 sepals and/or sepaloid stamens.