LSU AgCenter's Weekly Message

What to Do After the Cold Weather

We just experienced the coldest temperatures many of us have ever seen in Louisiana. I lived in central North Carolina for eight years, and 8 degrees F is the coldest I remember it being. While it didn’t get quite that cold at my house this week, it did reach that or a lower temperature in some parts of southern Louisiana. Doubtlessly, there will be much plant damage and death in the upcoming year.

Some good news is that snow acts as insulation. The fact that we experienced our coldest temperatures after we had a blanket of snow on the ground was helpful. Plant roots had some additional protection, beyond what’s provided by soil alone, on our coldest night. This is likely to have helped some plants that regrow from roots survive.

Another thing in our favor is that this occurred in the middle of winter, when plants were more acclimated to cold than they would have been in the late fall or in early spring, when plants had started to resume growth.

I expect that most of our native plants will be okay, even if they sustain some injury. There have been periods of intense cold in history. Of course, the finer points of where things are native may become important. For example, live oaks are native to coastal Louisiana, but we plant them north of the range in which they grew in the wild.

Plants that are marginally cold hardy here very likely sustained damage.

Parts of herbaceous (non-woody) plants that are brown and obviously dead can be cut back soon, though there doesn't need to be a rush to do so, and leaving some of the plant tissue may help protect them from cold weather later in the season. (Furthermore, pollinators and other beneficial insects often live in perennials’ dead stems. Based on this, it’s been suggested to leave the first 1 to 2 feet of dead stems for insect habitat.)

For woody plants and palms, waiting is advised.

On citrus trees, you may not be able to tell the full extent of cold damage until sometime in the summer. Branches or trunks with injured shoots may end up putting out new growth. Likewise, a cold-damaged tree may put out flushes of new growth that later collapse. Waiting until July or August, after the second annual flush of growth has occurred, gives you more time to see the full extent of cold damage. At that time, you can remove dead wood.

Also remember to remove rootstock growth from below the graft union as citrus plants recover. Most rootstocks have trifoliate leaves (leaves with three leaflets), so their foliage looks different than that originating from the scion (top part of the grafted tree).

When the time comes to fertilize citrus trees in late winter or early spring, if it appears that you have cold injury, you can reduce the amount of fertilizer in proportion to the part of the tree that appears damaged and, instead of applying it all at once, divide the total amount of fertilizer up into several smaller applications. Be sure not to fertilize after the end of June, though, since late fertilizer application can predispose citrus trees to cold damage the following winter.

On cold damaged palms, it’s recommended to let brown leaves remain until no further hard freezes are likely to occur. Survival of palms depends on survival of the growing tip (meristem) at the top of the plant. Dead or injured leaves can still help protect the growing tip from remaining cold events.

Since palms do not put out new growth until later than many other plants, wait until July to determine whether or not a palm is dead.

For all plants that survive but have cold damage, provide good care during the upcoming year to help them recover.

Let me know if you have questions.

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Dr. Mary Helen Ferguson is an Extension Agent with the LSU AgCenter, with horticulture responsibilities in Washington and Tangipahoa Parishes. Contact Mary Helen at mhferguson@agcenter.lsu.edu or 985-277-1850 (Hammond) or 985-839-7855 (Franklinton).