Using Sprinklers to Protect Blueberries From Spring Freezes

Many Michigan fruit growers, especially blueberry growers, use sprinkler systems to protect their crops during spring freezes. Sprinklers are very effective under certain circumstances but can increase injury if used at the wrong time. Sprinklers used for irrigation do not protect below 23-24 degrees Fahrenheit. If the system fails due to cold or wind, the blueberry blossoms 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 to keep the temperature in the ice right at the freezing point –32 F. When water goes from a liquid to a solid, it is an exothermic reaction which means that it releases heat. If you keep the ice wet, the ice temperature will stay at 32 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 When using sprinklers to help protect from frost injury, it’s important to understand that you need to keep the ice wet, and the point when your system won’t be able to keep the ice wet anymore in order to properly 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 F with no wind or 24 to 25 F with a light wind. More water is needed to protect at lower temperatures and higher wind speeds (see Table 1).

Growers should only use sprinklers to protect a crop from freezing, when the temperature range for protecting the crop is relatively narrow, from 24 to 32 degrees F. It's important to keep this range in mind because if the temperature gets a little colder than predicted, we could cause more damage than if we had not turned on the system. Once we turn on the system, we need to keep it on until the temperatures are above freezing or you will cause a lot of damage as the temperature of the ice goes down colder than outside the irrigated area.

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