Keeping freeze damage away from fruit trees and plants in early spring vary from commercial orchards to backyard gardeners. Cathy Isom tells us how to protect fruit buds and blossoms from early spring freeze.
From: Michigan State University Extension
Using sprinklers to protect plants from spring freezes
Many Michigan blueberry and strawberry growers use sprinkler systems to protect their crops spring freezes. The system is also used by some apple and grape growers. Sprinklers are very effective under certain circumstances, but can actually increase injury if used at the wrong time. Sprinklers used for irrigation do not protect below 23-24 degrees F. If the system fails due to cold or wind, the blueberries will get much colder than in areas where you are not sprinkling.
When you use sprinklers to prevent freezing injury, you are using the energy that water releases when it freezes, and changes from a liquid to a solid, to keep the temperature in the ice right at the freezing point – 32 degrees F. As long as you keep the ice wet, the ice temperature will stay at 32 degrees F. If the ice dries out and water starts to evaporate from the ice, the ice will get colder than the air temperature as it evaporates.
Protection with sprinklers
If you understand that you need to keep the ice wet, and when your system will fail to keep the ice wet, you will understand how to use your sprinklers to prevent freeze injury. The freeze protection from sprinkler systems is limited by the irrigation rate. Most sprinkler systems in Michigan are designed to provide about 0.12 to 0.15 inches of water per hour. This volume protects plants to about 22 degrees F with no wind or 24 to 25 degrees F with a light wind. More water is needed to protect at lower temperatures and higher wind speeds (see Table 1).