Question:
Will fruit trees be seriously harmed if they begin to leaf out or flower and are then subjected to freezing temperatures?Answer:
Freezing temperatures don’t harm dormant plants. In some years, warm late winter temperatures can cause some fruit trees to break bud, leaf-out, or develop flower buds earlier than normal. The inevitable below-freezing temperatures that follow in early spring, however, can damage new spring growth, especially flowers. As flower buds begin to swell, they become increasingly vulnerable to cold temperatures. They are most vulnerable just before, during, and after bloom. 
The extent of damage will be determined by the plant species, stage of flower development and temperature. Apricots and peaches are more prone to damage from a spring freeze as they bloom earlier than apples, pears and tart cherries. At full bloom, a temperature of 28 degrees Fahrenheit will kill approximately 10 percent of the flowers on apple trees, while a temperature of 25 degrees will kill approximately 90 percent of the flowers.
A late freeze may drastically reduce the size of the fruit crop. However, the trees themselves should not be seriously harmed.
