Now that we’ve been getting some cold weather, many gardeners have asked me about the susceptibility of their citrus trees to cold temperatures. I’m going to have to say “it depends,” but the bottom line is that if you have citrus trees in your yard, then it is important to understand how the different ranges of cold temperatures affect your citrus trees.
Among the citrus types most easily killed or damaged by freezing weather are lemons and limes. Temperatures in the high 20s will kill or severely damage these plants, with the extent of the damage largely depending on age, location, and whether or not the tree had hardened off prior to the freeze event.
Sweet oranges and grapefruits are somewhat more cold-hardy and usually require temperatures in the mid-20s before sustaining major damage to large branches.
Mandarins are quite cold-hardy, and can usually withstand temperatures in the low 20s without undergoing significant wood damage.
However, the highest degree of success and greatest satisfaction in growing citrus in Georgia will be realized with the satsuma. It will withstand colder temperatures, produce more consistent crops over a longer period of time and requires less cold protection than other types of sweet citrus.
Ultimately, among the edible types of sweet citrus, the satsuma and kumquats have the greatest degree of cold hardiness. And when properly hardened, bearing trees will withstand temperatures as low as 20 degrees Fahrenheit without appreciable wood damage.
Note that the temperature ranges I mentioned above are only referring to leaf or wood damage. Citrus fruits, on the other hand, easily freeze at 26 to 28 degrees F, especially when these temperatures last for several hours. A longer duration of freezing temperatures is required to freeze grapefruit than sweet oranges, and tangerines and satsuma fruits are more easily frozen than either of the former.
Now, the particular temperature at which tissue of a given plant will freeze and the degree of the damage sustained is when the “it depends” factor really comes into play, as these are functions of a number of factors in addition to the species and variety involved.
Some of the more important factors to consider are:
The freezing temperature reached;
The duration of the minimal temperature;
How well the plant became hardened or conditioned before freezing temperatures occurred (the freezing point of tissue of a hardened citrus plant might be 5 to 6 degrees lower than an unhardened plant);
If the tree has fruit (trees with a good fruit crop are less hardy than those with no fruit);
Age of plant (a young plant cannot withstand as much cold as a more mature tree);
Whether the plant is wet or dry (the killing temperature is 2 to 4 degrees lower for a dry citrus plant);
Healthy trees are hardier than diseased trees.
Another complicating factor contributing to observations by some that citrus plants seem to freeze at higher temperatures in some years is the difference between air (ambient) temperatures and leaf (tissue) temperature.
On a windy night with clear or cloudy skies, leaf temperature will be about the same as air temperature. On a cold, clear night with little or no wind movement; however, leaf temperature can easily drop several degrees (3 to 4 degrees) below the air temperature because of cooling caused by frost.
Thus, under the latter circumstances, while the minimum air temperature on a given night may have only been 25 degrees, actual leaf temperature of the plants may have reached 21 to 22 degrees. The critical temperature is that of the leaf or fruit and not the ambient air temperature.
Whether your tree has grass growing under it will also influence the temperature. Research data provided by Louisiana State University indicated trees growing on bare ground have a higher probability of survival than trees growing in turf areas. The reason for this is that heat from the ground can radiate upward into the tree’s canopy. The difference in the canopy of the tree can be up to 5 degrees, which can mean a great deal if that 5 degrees is the difference between your fruit freezing or not.
As you can see, I mean it when I tell you “it depends” when you ask me how your citrus tree will weather a freeze event. However, a general standard to follow is to protect citrus trees when the temperatures is expected to go below 27 degrees for an extended period, keeping in mind that citrons, lemons and limes are most easily killed by freezing temperatures.
The good news is before the cold snap, if temperatures had been on the cool side for a while and citrus trees had hardened off and were fairly dormant, then the damage may not be as severe. Citrus trees can better withstand cold weather when they are dormant.
If you suspect your trees do become injured by a freeze, no immediate action is required. There is no benefit to pruning the plant until spring growth commences, and the full extent of injury is manifested. Pruning might actually be counterproductive by stimulating faster bud activity before the danger of additional frost/freeze events has truly passed.
Do you want to grow your own citrus but you don’t know how to get started? Do your trees have pest issues during the growing season?
If you said yes, consider signing up for the Georgia Citrus: Backyard Basics Workshop! Liberty ANR agent, Ashley Hoppers, will walk you through the different types of citrus you can grow, and how to manage them and protect them from freezing weather. You’ll also learn about the deadly disease, Citrus Greening, and have an opportunity to assist your county agent with some citrus research!
To register for the Georgia Citrus Backyard Basics Workshop, please contact the Liberty County Extension office at 912-876-2133, or come by the office at 100 Main Street, Hinesville. We are located on the first floor in the Historic Courthouse You can learn more and follow updates about the workshop on our Facebook Page at facebook.com/LibertyCounty4H.