Estimation of cold hardiness of Douglas‐fir and Engelmann spruce seedlings by differential thermal analysis of buds*

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Abstract
SUMMARY: Low temperature freezing points of conifer buds were determined by differential thermal analysis and were compared to results obtained in whole plant freezing tests of the same seedlings. To obtain well‐defined, meaningful exotherms, it was necessary to nucleate buds externally. The low temperature exotherms for buds occurred at temperatures very close to the lowest which seedlings tolerate with no visible injury. Thus, for Engelmann spruce and Douglas‐fir, differential thermal analysis may provide a convenient prediction of containerised tree seedling hardiness.