FLOWERING OF LEUCANTHEMUM X SUPERBUM SNOWCAP IN RESPONSE TO PHOTOPERIOD AND COLD TREATMENT

'Snowcap' Shasta daisy [Leucanthemum x superbum Bergmans ex. J. Ingram (syn: Chrysanthemum xsuperbum, C. maximum)] was grown under various p hotoperiods and temperatures to determine their effects on flowering. In the first experiment, plants were held for 0 or 15 weeks at 5 degre es C and then were grown at 20 degrees C under the following photoperi ods: 10, 12, 13, 14, 16, or 24 hours of continuous light or 9 hours wi th a 4-hour night interruption (NI) in the middle of the dark period. Without cold treatment, no plants flowered under photoperiods less tha n or equal to 14 hours and 65% to 95% flowered under longer photoperio ds or NI. After 15 weeks at 5 degrees C, all plants flowered under all photoperiods and developed three to four or 10 to 11 inflorescences u nder photoperiods less than or equal to 14 or greater than or equal to 16 hours, respectively. To determine the duration of cold treatment r equired for flowering under short photoperiods, a second experiment wa s conducted in which plants were treated for 0, 3, 6, 9, 12, or 15 wee ks at 5 degrees C, and then grown at 20 degrees C under 9-hour days wi thout or with a 4-hour NI. Under 9-hour photoperiods, 0%, 80% , or 100 % of plants flowered after 0, 3, or greater than or equal to 6 weeks a t 5 degrees C, and time to flower decreased from 103 to 57 days as the time at 5 degrees C increased from 3 to 12 weeks. Plants that were un der NI and received greater than or equal to 3 weeks of cold flowered in 45 to 55 days. For complete and rapid flowering with a high flower count, we recommend cold-treating 'Snowcap' for at least 6 weeks, then providing photoperiods greater than or equal to 16 hours or a 4-hour NI during forcing.