Potential Impacts of Shade Treatments on Dormancy of Overwintering Redbud (Cercis canadensis L.) Trees at Southeastern Nurseries

Dormancy accrual is an important process in mitigating the abiotic stressors of overwintering trees at ornamental nurseries, with frost-injured tree crops at heightened risk of ensuing biotic insect and disease attack. As mean global temperatures rise, overwintering nursery crops may lose dormancy earlier. Using potted eastern redbud (Cercis canadensis L.) trees placed under two types of shade cloth, under full sun, or in walk-in coolers, we measured stem, air and root zone temperatures, accrual of chill hours and mean time to bud break at two sites. While there was no significant difference between the two shade treatments, shade cloths did moderate both high and low temperatures to which trees were exposed. Differences in mean time to first bud break were observed from shaded trees versus those in full sun at each site. It may be useful to alter our shading design to continue protection from overnight lows while preventing excess warming from daytime highs, and thus promoting dormancy and preventing frost exposure in some regions, but further tests will be required. Species used in this study: eastern redbud (Cercis canadensis L.).