Determining the Flowering Requirements of Two Aquilegia Cultivars

Flowering of the herbaceous perennial Aquilegia is generally considered to require vernalization after seedlings are mature, whereas photoperiod has little or no effect. We performed experiments to determine the flowering responses for two Aquilegia x hybrida varieties, one of which reportedly has reduced cold requirements. Seedlings of Aquilegia 'Origami Blue and White' and 'Winky Double Red and White' with three to five leaves were either placed directly into a 5 degrees C cooler with low-intensity lighting for 9 hours/day or transplanted to 13-cm containers and grown (bulked) for 0, 3, or 6 weeks at 20 degrees C under 9-hour short days (SDs) or 16-h long days (LDs). Plants were then cooled at 5 degrees C for 0, 5, or 10 weeks and placed in a common forcing environment at 20 degrees C under LDs. Flowering response of the two cultivars differed markedly. All Aquilegia 'Origami Blue and White' plants placed directly into the forcing environment flowered and in a mean of 93 days. Flowering percentage of plants cooled in the plug tray decreased with increasing duration of cold treatment, and only 15% flowered after a 10-week cold treatment. All plants bulked for 3 or 6 weeks before cold treatment flowered after 25 to 36 days in the forcing environment. Adding bulking and forcing time together, time to flowering of 'Origami Blue and White' was complete and most rapid (62 days) when plants were bulked for 3 weeks under SDs and then forced under LDs. In contrast, no 'Winky Double Red and White' plants flowered without cold treatment, and 6 weeks of bulking followed by 10 weeks of cold was required for 100% flowering. These results indicate that 'Origami Blue and White' has a relatively short juvenile phase and flowering was promoted by SD bulking or cold treatment, whereas 'Winky Double Red and White' has a longer juvenile phase and requires cold for flowering.