By Deborah Birge; Fort Bend Master Gardener, Citrus Specialist
We may still be slogging through high temperatures and relentless humidity but it is time to begin thinking of winterizing our citrus trees. But, before we do that let’s take a look at how our trees are affected by the cold.
Lemons, limes and citrons are cold hardy to the high 20’s. All oranges, mandarin, grapefruit, tangerines and tangelos are hardy to the mid-20’s, with kumquats and satsumas the most cold hardy, with-standing temperatures in the low 20’s. However, timing and duration are everything.
A satsuma will sustain freeze damage if the temperatures dip for several hours to 18 degrees in December. However, that same satsuma could withstand the same temperatures for the same duration if it froze in February. Why? Because the tree had time to harden off and go dormant. So, even though you may have a tree that will handle 15 degrees, as some of the new Arctic varieties claim, if the very cold weather is too soon in the season, you would do well to protect your tree. Additionally, the cold hardiness of a tree will be tested when wind and rain are involved with the freezing temperatures. Both make the situation more dire for the citrus grower. That said, what steps can we take to help insure the survival of our citrus?
*Firstly, take a long look at your tree. Does it look healthy or stressed? If stressed, look for the reason. Too much water, too little light, and too little feeding can result in stress. If the stress is too much water, begin to taper off on watering. Ideally, citrus should not be watered in winter unless it is containerized or there is a drought situation. If the stress is too little light, consider trimming overhanging trees in the Spring or moving the tree. If the stress is nutritional, give the tree a very light feeding. No more than about one fourth of the recommended feeding. Late summer is still feeding time for leaf miners and the Asian Citrus Psyllid. A late flush of new leaves is like laying a buffet for these pests.
*Look for pests. Most typically, you will find scale, mealybugs, or aphids and ants. Scale and mealybugs can be dislodged with a strong spurt of water or an insecticidal soap. Aphids and ants work together so must be dealt with together. If you don’t eradicate the ants, the aphids will return.
*Prepare the tree floor. Bare soil will absorb and then release more heat than soil covered by grass or mulch. If you have either, remove it from under the tree outward to the dripline or outermost limbs of the tree. Do be careful of the shallow feeder roots when working around the base of the tree. Work carefully so not to damage these important roots. If the tree is grafted and is less than four years old, a proven method of graft protection is to mound soil, not mulch or compost, around the trunk of the tree up past the graft and lower limbs. This mound should be installed in late November and removed in March. A light application of a copper based fungicide to the trunk before installing the mound will help protect the trunk. After removal, be sure to wash the trunk clean of all remaining soil.
*Gather your freeze protection materials. Nothing worse than hunting for equipment when a freeze is coming. A good arsenal might include micro-cloth or tarps for covering, Christmas lights or a shop light for raising the temperature, while some even use grills and propane heaters. There is a new tool for the arsenal called antitranspirant spray. This is a polymer spray that helps the leaves from losing moisture. Some find it effective for freeze protection and drought protection. However, the cost is very high so one would need to weight the cost against the gain.
Now that we are prepared for the freeze, what to do when one is eminent? Remember that we now have bare ground under the tree. Water that well. Moist ground will absorb the heat of the sun and retain it longer. Cover and add lights as desired. Remember to not put plastic directly on the tree. This will cause more burn than if you use a cloth material next to the leaf, then plastic, if desired. If you do use plastic, remove it as soon as the freeze lifts or the ice begins to melt. Cloth can stay for an indefinite time.
A common question is whether to harvest exiting fruit when a freeze is predicted. It’s helpful to re-member that most predicted freezes do not occur. So, plan to leave the fruit on the tree, only harvesting the following day IF the fruit has frozen.
In our next article we will discuss After Freeze Dam-age Care. Let’s hope this will not be needed by any of us. Enjoy the winter!