When winters are too mild, spring growth is delayed, irregular, and slow. These factors extend the period of blooming, thereby increasing the possibility of frost injury. On the other hand, extreme cold during winter dormancy may kill the fruit buds. Winter weather rarely threatens hardy 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.
As the fruit buds grow and open, they become more susceptible to injury from frost. 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. Protective coverings may be effective, such as floating row cover material or old bedsheets. During spring frosts, some commercial growers heat their orchards, but this method is impractical for home gardeners. Ice that forms on buds provides an insulating effect until temperatures rise above freezing.