When winters are too mild, spring growth is delayed, irregular and slow. These factors extend the period of blooming and, thereby, increase the possibility of frost injury. Extreme cold during winter dormancy may kill the fruit buds. Winter weather rarely threatens apple, pear, plum and sour cherry varieties. Sweet cherry trees, however, are relatively sensitive to cold until they become dormant.
Peach trees are very vulnerable to cold weather.
Their buds can be killed by midwinter temperatures around 10 o F below zero. The stone fruits, cherry, peach, plum and nectarine, can lose cold hardiness due to extended midwinter warm periods. Damage to the flower buds can be extensive, especially if the warm period is followed by a very cold period. As the fruit buds grow and open, they become more susceptible to frost injury. When a heavy frost is expected, covering the trees will sometimes prevent bud or blossom injury, provided temperatures do not fall too low and the cold weather is of short duration.