Storage treatments for very early forcing of narcissus

Summary

Experiments are described on storage treatments for forcing three cultivars of narcissus. For early-lifted, high-temperature treated bulbs a range of temperatures and durations for cool storage was investigated. A third variable examined was the time of starting cool storage, relative to the completion of flower differentiation within the bulb; between high-temperature treatment and cool storage bulbs were stored for variable durations at 17°C. Successful, rapid flowering was achieved after a minimum of 15 weeks of cool storàge, and a shorter duration in the glasshouse could be achieved by extending the duration of cool storage by 1-2 weeks. Two weeks extra cold resulted in a later flowering date. The optimum temperature was 9°C; at 5°C the stems were shorter. Earlier blooms (early-to late-November, depending on cultivar and experiment) could be obtained following shorter cool storage (12-14 weeks), but these were associated with shorter stems, smaller flowers and an extended glasshouse period. There were no indications of benefits to flower quality from a storage period at 17°C, to allow the completion of flower differentiation (Stage Pc), after high-temperature treatment and before starting cool storage. Satisfactory flowering was obtained following starting cool storage as early as Stage PI (first whorl of perianth segments visible). The use of accumulated day-degrees below 30°C was a useful guide to assess the satisfaction of the cold requirement, with 2000 units needed to obtain flowers after 30 days at 16°C, and 2250 for flowers in 21 days.