Citrus and Freezing Temperatures

Roy Dunn, Sr.
December 19, 2007
December 21
December 21, 2007
Roy Dunn, Sr.
December 19, 2007
December 21
December 21, 2007

The cold weather we typically receive now through January can cause problems for home and commercial citrus in our area. It is important to know what the critical temperatures are and the factors affecting them.

Among the citrus types that are most easily killed by freezing temperatures are citrons, lemons, and limes. Temperatures in the high 20s will readily kill or severely damage these plants. Sweet oranges and grapefruit are somewhat more cold hardy and usually require temperatures in the mid-20s before incurring major damage to large branches. Tangerines and mandarins are quite cold hardy, usually withstanding temperatures as low as the low 20s before significant wood damage occurs. But among the edible types of sweet citrus, the satsuma has the greatest degree of cold hardiness. Kumquats are also among the most cold hardy.


Properly hardened bearing trees will withstand temperatures as low as 20 degrees F without appreciable wood damage. Temperatures at ground level can be several degrees colder than temperatures around the canopy of the tree, especially if there is no wind.


Keep in mind that the temperature ranges given above refer only to leaf or wood damage. Citrus fruits easily freeze at 26 to 28 degrees F when these temperatures last for several hours. Further, a longer duration of freezing temperatures is required to freeze fruits of grapefruit as compared with sweet oranges. And tangerines and satsuma fruits are the most easily frozen of the common citrus.

The particular temperature at which tissue of a given plant will freeze and the degree of the damage sustained are functions of a number of factors in addition to the species and variety involved. Some of the more important are the following:


* 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 may be 5 to 6 degrees lower than an unhardened plant.)


* Age of plant (A young plant cannot withstand as much cold as a more mature tree.)


* Healthy trees are more hardy than diseased trees.

Another complicating factor contributing to observations by some that citrus plants seem to freeze at higher temperatures in some years than others is the difference between air (ambient) temperatures and leaf (tissue) temperature.


On a windy night with clear or cloudy skies, leaf temperature will be approximately the same as air temperature. However, on a cold, clear night with little or no wind movement, leaf temperature can easily drop several degrees (3 to 4 degrees F) below air temperature because of radiation heat loss. Thus, under the latter circumstances, while the minimum air temperature on a given night may have only been 25 degrees F; actual leaf temperature of the plants may have reached 21 to 22 degrees F. The critical temperature is that of the leaf or fruit and not the air temperature itself. Trees with a good fruit crop are less hardy than those with no fruit.


Research from the LSU AgCenter has noted that trees growing on bare ground have a higher probability of survival as opposed to trees growing in turf areas. The heat from the ground can radiate up on bare areas as opposed to being trapped in by turf areas. The difference in the canopy of the tree can be up to five degrees F.

We generally recommend you protect your citrus when the temperatures will be below 27 degrees F for an extended period of time. This protection must:


* Entirely cover the plant trying not to touch the foliage

* Extend all the way to the ground

* Must be removed the next morning once temperatures begin to rise

You can also install small lights such as Christmas lights on the trees to increase the temperature around the trees. Freeze damaged trees should not be pruned until the extent of the cold damage has been determined. Normally, the damage is not evident until mid spring.

Winter Gardening Tips

Houseplants are often overlooked when it comes to proper care and maintenance. This is especially true during the holidays when family time is the priority. By this time, houseplants need a little change in their environment, such as more light and humidity. If a nice sunny warm day comes along, set the plants under indirect sunlight on the porch or patio.

The yellowing of houseplant leaves is fairly common in winter. Possible causes are poor drainage, over-watering, gas fumes, poor light, and lack of plant food or a combination of these problems.

For vegetable gardening, this is a good month to plant beets, carrots, radishes, turnips, mustard, spinach, kale, Swiss chard and kohlrabi.

Some vegetables can be planted as seed in cold frames, hot beds or greenhouses for transplanting to your garden later. These include broccoli, cauliflower, cabbage, Chinese cabbage and lettuce. In our area, you also can plant tomatoes, eggplants and bell peppers in hot beds or a greenhouse during January.

If you want tomatoes in your spring garden, you might try Amelia, BHN 444, Champion, Creole, Celebrity, Merced, Mountain Pride, Mountain Delight, Better Boy, Jet Star, Supersonic B and Fantastic. For pink fruit types choose either Pink Delight or Pink Girl. Good canning varieties are Royal Chico and Roma. First Lady is an excellent indeterminate variety for our region.

If you’d like to grow Irish potatoes, you can begin planting them around the middle of January in our area. The recommended red skin varieties are Red LaSoda, LaRouge, Norland and the new Fontenot. Red LaSoda is the most popular variety in our area. The recommended white skinned varieties are LaChipper, LaBelle and Atlantic. Unfortunately, all these varieties are in short supply and may be difficult to find.

It is important to remember to put out pre-plant fertilizer at the rate of seven to eight pounds of 8-8-8 or 13-13-13 per 100 feet of row. Keep in mind that you will need to side-dress with ammonium nitrate (33-0-0) at the rate of 3/4 pound per 100 feet of row when the plants reach six inches in height. This is a general recommendation relating to soil fertility. You can take a soil sample now and determine the plant needs based on the soil pH, nutrients available in the soil as well as the soil texture. Soil test results can be received in 5-10 business days for a cost of $7.00 per sample.

You will need seven to eight pounds of seed potatoes to plant a 100-foot row. Once you have secured your seed potatoes, you will need to make sure they are fresh and disease free. Check the potatoes and check for soft, bad smelling seed and remove. The seed potatoes have to be cut into pieces about the size of an egg. Make sure each seed piece has at least one eye, as this is where the new plant will originate. Place the cut side down and space seed pieces about 12 inches apart for best results.

Check out the Vegetable Planting Guide at www.lsuagcenter.com.

For more information on winter cold protection, go www.lsuagcenter.com or come by the Lafourche Parish Extension office located on 402 West 5th Street in Thibodaux or call me at 985-446-1316.