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U.S. Department of Agriculture USDA Forest Service Southern Regional Extension Forestry Southern Regional Extension Forestry

Chilling and Photoperiod Affect Dormancy of Cottonwood Cuttings

Unrooted cuttings of 23 cottonwood clones were chilled at 1.6°C for periods of 0 to 90 days and planted in a greenhouse under normal and extended (16 hr.) photoperiods. The clones varied in flushing response to chilling treatment. Some required only 40 to 60 days of exposure to cold temperature to reach a point where additional chilling had no significant effect on reducing flushing time, while others continued to respond at 90 days. There were no distinct geographic trends associated with this variation. The extended photoperiod was effective in breaking bud dormancy only when the buds were not adequately chilled. Even short exposure to cold temperature (50 days) was sufficient to overcome any significant photoperiod's effect. These results suggest the possibility of using fast-growing northern selections of cottonwood with low "chilling requirements" for planting in the South.

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Author(s): James W. Chandler, Bart A. Thielges

Publication: Tree Improvement and Genetics - Southern Forest Tree Improvement Conference - 1973