Freeze damage to orange tree

Well, it happened, and I know pretty much all of us are dealing with the same issue.

Despite our best precautions many of us were burned by the arctic blast over Christmas. Lows around 20 degrees isn’t our normal, but not out of question. One issue we faced was the lack of cold weather in the run-up to our visit from Jack Frost.

Eighty-degree highs in early December gave plants a false since of security. Winter likes to surprise us, though. One of the questions I was asked before the freeze was, “How do I protect my citrus trees?” The question I’m being asked now is, “What do I need to do with the freeze damage?”

While we are seeing crispy brown leaves on most citrus trees, I’m not really concerned about trees dying from the cold, especially healthy trees that were already established. Most of our mature citrus trees that are planted in a good location can survive short bursts of cold weather with minimal protection. One issue we often see is cold damage caused by improper protection.

Plants are warmed by the sun and radiant heat given off by the earth. Once the sun sets, soil continues to radiate heat, providing a few degrees of warmth.

Many people automatically reach for a blanket or covering for trees or plants. This is only successful if used correctly. Any type of cold weather covering needs to extend all the way to the ground to trap radiant heat from the Earth. Plastic coverings touching vegetation transfer freezing temperatures to the vegetation causing tissue to freeze or “burn.”

After a cold weather event, the first reaction is to want to cut off what appears to be dead. The best thing to do, though, is wait and see. I know it looks unsightly, but we are still a few months away from determining the full extent of freeze damage. You don’t want to hastily remove branches that could help provide the rest of the plant protection from possible cold weather we may experience before spring.

Generally, it is safe to prune freeze damage once new grow has budded out. This may mean waiting until June. Normal pruning on citrus trees is usually done in February to remove downward growing limbs, limbs that have become excessively tall, or to open the canopy to make harvesting easier. Never cut back a citrus tree to below the graft union located a few inches above the soil surface and easily seen as a scar circling the trunk.

All citrus trees sold in Louisiana are grafted to a hardy rootstock, typically trifoliate orange. This rootstock is more tolerant of our soil conditions, and it is more tolerant of freezing temperatures.

Often people ask if they can grow a satsuma or lemon from seed. Yes, you can, but growing from seed and planting citrus not grafted lessens the tree’s ability to thrive in our soil conditions and winter temperatures. These trees also take longer to produce (assuming they live that long) and the fruit will likely be different from the parent tree. Grafting uses wood from mature trees to shorten the time to fruiting and keep fruit quality consistent.

If you do see thorny branches growing in the tree, examine them carefully. If they emerge from below the graft union, this is likely the trifoliate rootstock that has sprouted. Go ahead and prune that out. Be careful you have the right branches though. While all citrus limbs can produce thorns, limbs of trifoliate rootstock are much thornier and have different shaped leaves. As the name suggests, the leaves are arranged in groups of three.

Patience and careful examination of your citrus trees can prevent unnecessary pruning, hastily removal of trees on the rebound, or leaving trifoliate trees to grow in place of a desirable tree.

Clark Robertson is the assistant county agent for horticulture for Livingston and Tangipahoa parishes. For more information on these or related topics, contact Clark at (225) 686-3020 or visit www.lsuagcenter.com/livingston.

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