Blueberries, like most temperate zone plants, become dormant during the winter, allowing them to survive the cold. As days become shorter and temperatures lower throughout the fall, blueberries’ growth slows and cold hardiness increases.
While blueberries that become fully dormant don’t typically have serious damage from the cold, methods can still be taken to improve their chances of surviving.
Passive Blueberry Freeze Protection
Planting cultivars that flower late reduces freeze risk. However, these late-flowering cultivars also ripen later, usually after prices fall.
It’s best for blueberries to be planted on low, cold land because those soils have high organic matter. Low land also provides more stable temperatures, unlike hills that could be five to 10 degrees warmer on clear nights with no wind.
Pruning immediately after harvesting can postpone next season’s flowering by one to two weeks.
Even though overhead irrigation systems are the most common and practical methods to protect blueberries from Florida freezes, a lot of water needs to be used for good protection.
Using water efficiently requires experience and close attention to the weather. Deciding if and when to turn on an irrigation system depends on the system’s capability, a crop’s development stage, relative humidity, temperature, and wind speed.
Alternative Protection Methods
Wind Machines and Helicopters
Both methods are based on the fact that strong temperature differentials occur on clear, calm nights. Temperatures within six feet of the ground may become much colder than temperatures higher up. By mixing these air layers, wind can raise the near-ground temperature by about 4ºF. On windy nights, this method is not practical because no temperature inversion develops.
Heaters are an effective—but expensive—method to protect blueberries from freezing. Heaters burn a gallon of fuel per hour, and costs may be more than $300 per acre for one night.
Experience seems to be the best way to learn how to protect blueberry crops during freezing events. Damage during freezes depends on the interaction of many factors, such as
- temperature, wind speed and dew point
- plant tissue hardiness
- physical conditions in the field
- weather before the freeze
- blueberry variety
Paying attention to the various conditions during freezes and their effects on crop damage will provide better knowledge of how to protect crops during future freezes.
To learn more about protecting crops from freezes, talk with your local Extension office to determine the best methods for your situation and location.
Adapted and Excerpted From:
P. Lyrene and J. Williamson, “Protecting Blueberries from Freezes in Florida” (HS968), UF/IFAS Horticultural Sciences Department (rev. 06/2015).