You may have heard that low temperatures can damage citrus trees and greatly impact the citrus industry—but did you know that the most common way to combat freezes in Florida is to encourage ice to form on and around citrus trees? It seems counter-intuitive, but here’s how irrigating trees can promote citrus cold protection:

• When water freezes, heat is released into the environment. This heat is called the heat of fusion (Parsons and Bowman 2013). This may sound strange—how is heat involved in freezing?—but think about what happens when ice melts. In order to melt, heat has to be added to the ice, and this heat comes from the environment surrounding the ice. In other words, when ice melts, heat is sucked out of the environment and goes into melting the ice. However, when water freezes into ice, the opposite happens, and heat is released back into the environment.
• So why is water freezing good for citrus trees? When ice forms on or near the tree, the heat released back into the environment can keep the tree “at or near 32⁰F” and out of the danger zone, 28⁰F or below (Parsons and Bowman 2013).

Citrus growers take advantage of the heat released when water freezes by irrigating their groves during cold weather events. Irrigating during freezes is a complex balancing act that factors in current weather data and forecasts, soil type, and type of tree (Jackson, Morgan, and Lusher 2015). But at the end of the day, trees can stay alive because of ice, not in spite of it.

References

Jackson, John L., Kelly Morgan, and William R. Lusher. 2015. Citrus Cold Weather Protection and Irrigation Scheduling Tools Using Florida Automated Weather Network (FAWN) Data. SL296. Gainesville: University of Florida Institute of Food and Agricultural Sciences. Accessed December 8, 2015. https://edis.ifas.ufl.edu/ss509

Parsons, L. R., and B. J. Bowman. 2013. Microsprinkler Irrigation for Cold Protection of Florida Citrus. HS931. Gainesville: University of Florida Institute of Food and Agricultural Sciences. Accessed December 8, 2015. https://edis.ifas.ufl.edu/ch182

Photo credit: Tyler Jones, UF/IFAS

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