Vernalization and devernalization of Campanula 'birch hybrid' and Leucanthemum xsuperbum 'Snow Cap'
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The influence of vernalization temperature and duration and devernalization treatments on subsequent growth and flower development of Campanula 'Birch Hybrid' and Leucanthemum x superbum Bergman ex J. Ingram 'Snow Cap' was determined. In the vernalization experiment, plants of 'Birch Hybrid' were vernalized at 0, 2.5, 5, 7.5, or 10 C for 2, 4, 6, or 8 weeks. 'Snow Cap' was vernalized at 0, 2.5, 5, or 10C for 2, 4, 6, or 8 weeks. In another devernalization experiment, plants of both species were moved to a high temperature (30/10C, day/night) growth chamber for 2 or 4 days at various times during or after the 6-week vernalization period. A 6-week vernalization was necessary to obtain 100% flowering in 'Birch Hybrid', and 8 weeks of vernalization decreased time to flower by 7 to 10 days compared with 6-week vernalization. Exposure to high temperature for 2 days during or immediately after vernalization did not devernalize 'Birch Hybrid' plants, while a 4-day exposure decreased flowering percentage in some treatments and delayed flowering by 7 to 10 days. There were no significant differences in flowering characteristics of 'Snow Cap' plants vernalized at 0 to 5C for 4 to 8 weeks. A 2-week vernalization at 0, 2.5, 5, or 10C or 4 to 8 week vernalization at 10C delayed flowering by 5 to 10 days compared with those vernalized at 0 to 5C for 4 to 8 weeks. Exposure to high temperature for 2 d did not devernalize 'Snow Cap' plants regardless of exposure times, but a 4-day exposure delayed flowering by 4 to 5 days in some treatments. Combined, the data indicate that 'Birch Hybrid' has an obligate 6-week vernalization requirement and 'Snow Cap' has a facultative 4-week vernalization requirement that can be fulfilled in the 0 to 10C range. Exposure to temperatures of 30C (9 hd-1) for 12 out of 42 days did not devernalize either species but in some cases caused a small delay in time to flower.
