The loss of container-grown nursery stock during winter months may be due to lack of root hardiness when exposed to cold temperatures. After Euonymus alatus `Compactus', Weigela florida `Java Red', and Hibiscus syriacus `Paeonyflora' reached midwinter hardiness, replicates of each cultivar were subjected to 12 hours of 21°C followed by 12 hours of 0°C each 24-hour period for up to 16 days. Controlled temperature freezing was conducted after each 48-hour period, with temperatures ranging from –6 to –27°C to determine the level of root hardiness. Plants were placed in a greenhouse environment to observe post-stress performance. Weigela was the most cold hardy, followed by Euonymus and Hibiscus. In general, the early accumulation of warming temperatures decreased root hardiness and delayed budbreak, with a noticeable loss of vigor. Results of this research will be presented.
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