Frost and Freezing

During freezing temperatures, ice crystals form inside of plant cells that rupture the cellular membrane, resulting in death of frozen tissues. Plants have developed many adaptations to avoid freeze damage. For instance, deciduous species shed their leaves and “harden off” succulent tissues before the first frost to avoid damage, and the cells of pine needles expel water into intercellular spaces to avoid intracellular ice crystal formation. However, early frosts in the fall or late frosts in the spring can catch trees off guard and unprepared for freezing temperatures. Newly expanding leaves in the spring are the most susceptible, as are actively growing tissues in the fall such as shoots that have not adequately hardened off. Freeze damaged tissues may appear bruised and water soaked, eventually turning brown or black. Dead tissues may eventually fall out of leaves, giving foliage a “shot-holed” appearance. Excessive rainfall in the fall can encourage trees to continue to put on new growth that may not adequately harden off before the first frost.