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  • Author or Editor: N. Curtis Peterson x
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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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The nursery industry continues to develop improved methods for successfully overwintering container-grown nursery stock. Experiments were conducted using several different species of woody ornamentals ranging from species known to be cold hardy to cold tender. Eighteen species were subjected to temperatures ranging from 20F to -20F and observed for post-stress performance and viability. Rates and timing of acclimation, mid-winter hardiness, and deacclimation of seven species were determined by examining the shoots for injury after subjecting them to controlled freezer conditions. The roots of the same seven species were exposed to three different overwintering systems: in a polyhouse, pot-to-pot above the ground, and pot-in-pot below the ground. Cold hardiness of root and shoot systems and the effects of warming temperatures on shoots were determined as well as the post-stress performance of each species. Results of this research will be presented.

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