Once we have bud break, we have to be very vigilant about frosty nights and mornings. When the temperature hits 36 degrees, we turn on the overhead sprinklers for frost protection.
The objective of frost protection with overhead sprinklers is to maintain a temperature of 32°F at the surface of the plant. One widely used method to achieve this is to apply and maintain a thin film of water on the ice-encased surfaces of the new buds. In principle, water is constantly applied to keep the ice at 31-32°F, which keeps the buds at 32°F. More specifically, when water is applied to the ice, a small amount of heat energy is released as the water freezes into ice. The energy required to turn liquid to solid – in this case water to ice – is called the heat of fusion. The amount of heat energy released when 32°F water is changed to 32°F ice is 144 BTUs per pound.