Karen Cambre, Sharpe, Kenneth W.
News article for December 11, 2017
It is very unusual weather when I open my door in south Louisiana and see snow four mornings in a row. In the snow I noticed lavender flowers from my Formosa azalea against that pure white background, an old fashion spring blooming azalea also confused about the weather.
Our unusual snow event also created a lot of concern for those with citrus still on the tree. The typical citrus owner wants to know the temperature that will cause damage to their fruit still on the tree. Unfortunately, there is no such concise answer and no two events are the same.
One variable is how cold it has been just prior to the cold front arriving. In this case we were at 80˚F just a few days prior. That means that the soil was still warm and radiating a lot of heat up around the plants. For cold protection the single best practice is to remove all mulch and vegetation from under the canopy of the tree and leave the ground bare. This will allow heat to radiate up and keep the tree warmer. It is usually one or two degrees that makes the difference. The other component of temperatures prior to a cold event is about dormancy. The more cold you have had prior to a freeze event, the better the plant has already hardened off and began to move into dormancy. An actively growing tree that has not received prior cold temperatures will be more vulnerable than one that has already received several frosts.
Duration of the cold is extremely important. The longer freezing conditions exist, the more potential damage. It is not that concerning to have a low of 28˚F if the temperature drops for only an hour or two just at daybreak and then warms up quickly. It is more concerning to have a cold event that has freezing temperatures for 6 or 8 hours. That duration will allow the tree and fruit to get much colder. It is like making ice in your freezer, when you put water in trays it does not freeze instantly; it takes some time for water to reach freezing temperature.
The exposure of the trees is also important. Trees on the south side of a building will receive less damage than those open to the north without a building or trees for protection.
It would seem that you should just go ahead and harvest all the fruit before a potential freeze, but citrus have some unique characteristics that make it more complicated. Unlike most other fruit, citrus will not continue to get ripe once it is picked. You will end up with tart fruit if you pick too early because citrus will not continue to get sweet after it is picked.
Satsumas are widely popular here because they are more cold hardy than any citrus except Kumquats. Satsumas are usually ripe by December 1st. I usually think about 27˚F as a threshold when you might want to pick the fruit and put them in the refrigerator.
We have a lot of Meyer lemons in our area. I do not recommend planting lemons or limes this far north because they do not take cold weather, but a Meyer lemon is the exception.It is much more cold hardy because it is a cross between a mandarin orange and a lemon with the cold tolerance of the orange and flavor of the lemon. It starts getting ripe in October but can have fruit on the tree until the first of the year. Lemons are considered ripe when they turn yellow. Unlike satsumas, lemons do not refrigerate well. If you have to pick a lot at once, your best option is to juice the lemons and place the juice in ice trays and freeze them. You can transfer the cubes to freezer bags and then take out as many cubes as needed throughout the year.
I occasionally find navel oranges, Louisiana sweet oranges and even a Blood oranges. Their fruit are more vulnerable because the fruit matures in December. The fruit will keep in refrigeration, but do not juice navels unless you are going to drink it shortly as their juice will become bitter when stored.