About Freezes and Cold Protection

Freezes play a crucial role in the citrus industry. A freeze can kill trees, damage fruit production, and sometimes be profitable due to shortages increasing the prices of the limited crop. The main side effect of a major freeze is groves moving southward. 

A freeze results from the importation to the state of large masses of air at subfreezing temperatures. Typically a freeze will last three days. The longer the citrus plant is cold, the more damage is caused which why a freeze does significantly more damage to the crop than an overnight frost. For Florida freezes may occur anytime during the state's coldest months which is between November 15 and March 15. Ziegler and Wolfe state that once the low atmospheric temperatures drop below 32 degrees Fahrenheit, the temperature at which water begins to freeze, injury to the citrus plant begins to occur. Some varieties of citrus can last at lower temperatures, but once the tissues inside the plant start to freezes damage to the tree, its foliage, and fruit start to occur. Older more mature groves tend to have a higher tolerance to freezes. Depending on the maturity and variety of the tree, this can be anywhere from 30 degrees to 26 degrees.

COLD PROTECTION

There is only a handful of tools and methods that have been created over the years to protect citrus groves from the cold. The citrus industry did not have to protect their crops for the first three centuries and with most severe freezes substantially spaced out, so citrus growers in Florida have had little time to experiment to discover the most effect methods to protect their groves. 

The first time grove-heating was done was during the 1899 freeze, although this was not a widespread practice since according to Larry K. Jackson, growers were more in “favor of covering trees with tents or cloth than heating trees in the open air.”

Today, heaters are typically spaced throughout groves. For groves using heating typically, there are 50 to 60 heaters per acre. Heating groves can be extremely effective if and only if there are not intense cold winds associated with the cold. Cold winds can carry the heat away, making it a waste a money to use heaters since a grower could still lose their crops.

A common method to protect against the fridge air and cold temperatures are actually by using water. If there is a constant stream of water falling on a grove, without flooding the plant, then the internal tissues of the trees can be protected. According to Ziegler and Wolfe, the cold air will cause the water to turn to ice on the tree, but the constant stream of water will prevent the tree’s temperature from falling below 32 degrees Fahrenheit.

During the 1962 freeze, growers tried to use water to protect the crops, but they could not find the right speed to disperse water on to the crops to protect them. This resulted in the destruction of several groves. Ziegler and Wolfe explain that even today this method is discouraged on the “fear of a repetition of the events of 1962.”

Other methods would include using wind machines or micro irrigation systems, but both of these options render similar results to the heaters and water options. All of these methods would have been available during the 1980s freezes.