Cold hardiness is defined as a minimum temperature at which a certain percentage of a random seedling population will survive or will sustain a given level of damage. (Open this attachment - Cold Hardiness Test) Changes in LT50 (lethal temperature for 50% of a population) are strongly linked to the seedling dormancy cycle and stress resistance and are influenced by seed source, nursery practices, and environment. The LT50 at lifting has been shown to correlate well with first-year survival and shoot growth.