Freezing Date and Duration Effects on Regrowth of Three Species of Container—grown Herbaceous Perennials

Abstract

Abstract Three species of herbaceous perennials were transplanted from 400 cell-size plugs to 400-ml containers and grown in a glasshouse at 25C day/20C night (78/68F) ± 2C (4F) until October 10. At that time glasshouses were programmed for ambient outdoor temperatures, but maintained above 3C (38F) ± 2C at night. Plants were exposed in controlled programmable freezers to four freezing temperatures [−5,−5,−11 and −14C (23, 18,12,7F)] on November 15,1995, and January 1, 1996. Plants were allowed to remain at each temperature for either 30 or 120 minutes. Plants were then returned to the glasshouse, and rated for survival and salability following 6 weeks regrowth at 15C (59F). The rating scale was subjective and ranged from 1 to 5 (1 = worst, 5 = best, 3 and above considered salable). Regrowth means of all three species declined as treatment temperatures decreased. Although freezing date had a significant influence on regrowth quality of Aquilegia and Dianthus, only freezing duration influenced Dianthus regrowth. Neither factor significantly influenced regrowth quality of Lavandula. Treatment temperature and its interaction with freezing date or duration was statistically significant for all three species. All plants remained marketable following exposure to −11C (12F).