Freezing injury is easier to identify and a lot more damaging than above freezing cold injury. It is caused by subfreezing temperatures. The impact of subfreezing temperatures may be felt from as little as one overnight episode or from a more sustained exposure episode. Plants subjected to subfreezing temperatures may exhibit ice formation in the vascular vessels, in the spaces between the cells and/or within the cells. The extent and pattern of ice formation vary with the plant tissue and its condition. Ice formation in the spaces between cells is usually not fatal, but it causes water to leave the cells, causing dehydration. If the freezing episode is cold and long enough, it can result in freezing within the cells. Internal or intracellular freezing ruptures membranes and leads to cell death.
Freezing damage begins with dehydration and ultimately ends in plant tissue death. Typical signs of freezing injury are a blackened/brownish discoloration or bleaching of plant tissue. The severity of the freezing damage depends on the type of frost injury and the plant parts affected. If the freezing injury kills a significant number of buds or cambial tissue, the plant may die outright or suffer so much crown die-back that it becomes unusable or unacceptable in the landscape. More commonly, however, freezing injury may be limited to flower buds and minor shoot dieback. This damage may require corrective pruning and time to allow the plant to grow out of the damage.
Freeze damage to a landscape plant.Information and photo from a section of "Abiotic Plant Disorders - Symptoms, Signs and Solutions A Diagnostic Guide to Problem Solving" by Robert E. Schutzki and Bert Cregg, Departments of Horticulture and Forestry, Michigan State University Michigan State University. Go to http://www.ipm.msu.edu/cat08land/pdf/9-19abiotic.pdf for the full factsheet with photos.
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