Growing Degree-day Requirements for Scheduling Flowering of Scadoxus multiflorus subsp. katharinae (Baker) Friis & Nordal
Containerized plants of Scadoxus multiflorus subsp. katharinae (Baker) Friis & Nordal were forced to anthesis under three environments of contrasting temperature. Flowering performance, growing degree-days (GDD) requirements for timing of anthesis, and the influence of cold storage (12 °C for 4 weeks) before forcing were evaluated. Total forcing time from the beginning of the experiment until anthesis decreased with warmer forcing environment, ranging between 129 and 86 days. Across all forcing environments, use of GDD was readily able to explain differences in time to anthesis resulting from both cold storage and forcing. Using a base temperature of 5 °C, GDD requirements between beginning of the experiment and anthesis was 1166 ± 124 GDD, emergence of the vegetative shoot and anthesis 1075 ± 118 GDD, and appearance of the tips of the leaf lamina and anthesis 883 ± 91 GDD. Using a base temperature of 11.5 °C, GDD requirements between appearance of tip of the involucre and anthesis was 180 ± 44 GDD, and the whole involucre being visible and anthesis 144 ± 42 GDD. In the next year, validation of the GDD requirements was achieved by subsequently forcing a second population of plants to anthesis for a specific date.