The cold hardiness of ten landscape pear cultivars and two pear species was evaluated in container- and field-grown plants during the dormant periods of 1991 through 1994. Timing and extent of acclimation by containerized plants overwintered in a temperature-moderated greenhouse was similar to that of plants growing in the field, indicating that containerized stock can be used for determining the hardiness of taxa lacking sufficient hardiness to survive outdoors in USDA Zone 4a. Among P. calleryana cultivars, ‘Autumn Blaze’ exhibited the best overall cold tolerance and greatest mid-winter hardiness [−34°C (−29°F)]. ‘Bradford’ was consistently the least hardy P. calleryana cultivar. All P. calleryana cultivars acclimated too slowly in the fall and or lacked sufficient mid-winter to survive in USDA Hardiness Zone 4a. Both P. salicifolia ‘Silver Frost’ and P. fauriei were hardier than the P. Calleryana cultivars on most sampling dates. P. ussuriensis was the hardiest taxon on all sampling dates and withstood −42°C (−44°F) by mid-December 1992. In field trials, only ‘Silver Frost’, P. fauriei, and P. ussuriensis survived exposure to −36°C (−32°F) in January of 1994.
Journal Series Paper number 21,127 of the Minnesota Agricultural Experiment Station. This research was partially funded by Horticultural Research Institute, Washington DC in 1991 from the Albert and Olga Bachman Grant and in 1992 from the Karl Junginger Grant.
2Scientist and Professor, respectively.