cold hardiness

Factors Influencing Cold Hardiness of Citrus

Daniel Cooper Cold Hardy, Georgia

cold hardiness

Jake Price, University of Georgia county Extension coordinator, recently reported on the factors that influence cold hardiness of citrus. Excerpts follow:


The most obvious factor is the variety of citrus. In order of cold hardiness, the three main classes of citrus are mandarins, sweet oranges and grapefruit. Acid types of citrus such as lemons and limes are the least cold hardy.


Citrus trees that are preconditioned or acclimated to cold temperatures before a freeze event will better endure a freeze. Trees that are actively growing before a freeze are more likely to be damaged by a freeze. Trees exposed to 25 degree temperatures in November are much more likely to suffer damage than if the same temperatures occurred in January. To help acclimate citrus trees, it is best to limit nitrogen fertility after August so the trees can slow their growth.


Rootstocks also influence cold hardiness of citrus. One particular rootstock, Poncirus trifoliata, is known for cold hardiness and can survive as far north as New England. This rootstock goes dormant at higher day and night temperatures than other rootstocks, therefore slowing the growth of the tree before winter. There are hundreds of different rootstocks. For more information, refer to the University of Florida’s Florida Citrus Rootstock Selection Guide, 4th Edition.


The age of citrus trees is important in cold hardiness. First year trees are more likely to experience freeze damage compared to older trees.


It is important to protect younger trees during the winter. Continuously applying irrigation to the trunks of citrus during a freeze can protect the trunk and scaffold branches. See more on freeze protection here.


The site where trees are located is also very important. Trees on southern or western facing slopes will survive better than trees facing north. Windbreaks will protect trees from advective freezes that blow away warmer air emanating from the ground or nearby structures. Trees planted on higher ground will survive better as cold air will flow downward to lower areas. Citrus trees planted in low areas are much more likely to experience freeze damage than trees planted on higher ground. 


Citrus trees exposed to a few hours of below freezing temperatures are less likely to experience freeze damage than trees exposed to freezing temperatures for many hours below freezing. Fruit can freeze when temperatures reach 28 degrees for several hours.


Another factor is tree health. Healthy, well-cared-for trees will better tolerate freezes than trees that are stressed by insects, diseases and lack of nutrients.


Harvest fruit as soon as possible as trees with heavy fruit loads are stressed and more likely to suffer from freeze damage.

In Georgia, most citrus trees will have some degree of damage from freezing temperatures after each winter, but normally the damage is minimal.

Source: Georgia Citrus Growers Association

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