Freeze Injury to Woody Plants 2021 Versus 1983
Published March 1, 2021 By KEVIN BASSETT
As one of the few certified arborists whose career spans the thirty-eight years between the 1983 and the 2021 cold-weather events, I’ve been asked to answer a few questions about what effects to anticipate on trees and plants from the extreme cold. There are a number of new species planted in North Central Texas and since many were introduced after 1983, little is known about their cold hardiness.
I hope the differences in the freeze this year versus 1983 were significant enough to lower the mortality rate and the severity of injury to plants and trees. For example, in 1983, the temperature dropped at a quicker descent to sub-freezing and the duration of intense cold was longer. This caused greater freeze damage to plants and trees. This year, the snow accumulation acted as an insulator which helped to moderate the temperatures that roots were subjected to. Snow may have been a saving grace for survival and the severity of injury to trees and plants.
This year, I found folks mitigated local micro-climates better, an important factor to a plant’s survival. In many cases, people better prepared their plants for freezing temperatures. Good soil moisture levels (reduces freeze damage and injury on plants), a layer of mulch (insulates plants and tree roots), plant covers (protect sensitive plants), lightbulbs, heat lamps, kerosene heaters, and smudge pots (keep plants warm) also helped prepare plants and trees for the extreme weather. This kind of preparation requires foresight and resolve to accomplish but it can make a difference in a plant’s survival.
I expect the full extent of the damage and mortality of some plants will not be known until May when Spring brings new hope. We should also see the positive feedback from trees by then, however, lingering effects may continue to present themselves as the growing season progresses. We will continue to see some tree mortality, especially for trees that were already stressed before the freeze but for those that wondered if the age of their tree would influence how it is affected, it should not. I recommend keeping an eye on freeze-damaged and injured trees at least for a year as they will be more vulnerable to insects and possibly some diseases.
The following are the answers to several specific questions people posed:
Palms, Pittosporum, and Lorapetalum- Expect severe injury and high mortality rates. At the minimum, expect the loss of most fronds on Palms. If the meristematic points where new leaves and roots develop are not damaged, the Palm may survive. Since Palm trees are not native to North Texas, it is risky to depend on them as a staple in your landscape. They may survive if you were able to successfully manipulate their micro-climate.
Palm trees are not cold hardy plants and most varieties will suffer a tremendous loss of their fronds with many not surviving.
Live Oaks, Magnolias, and Hollies- Not expecting severe injury or high mortality rates.
A Magnolia with freeze damage from the February 2021 weather event.
Live Oaks- Many have brown leaves and/or leaves that have shed. The browning or loss of foliage should not be a determining factor in deciding if a tree is dead or suffering. Many Live Oaks will put out a new set of leaves this Spring. When this happens, you can expect copious leaf drop from Live Oaks as the new leaves emerge and push off the old-damaged foliage. This is a normal transition for Live Oaks.
Brown leaves are a common site for Live Oak owners. Continue being patient and do not use the foliage of a tree as a barometer for its health. Most of the trees with dead or dropped foliage are showing promise and have new viable twigs and buds.
Be conservative with your approach to Live Oaks. Do not panic, it is best to wait and observe. So far, most Live Oak twigs and their buds appear viable.
In 1983, Live Oaks developed “ring shake”, recognizable as the bark and outer layers of trees separate from inner wood. We haven’t detected it this year, but if it happens, do not panic and pull the bark off your Live Oak. Pulling the bark off will expose the fragile underlying tissue. This is one reason many Live Oaks died in 1983, unknowingly destroyed in this manner. Trees left with loose bark in place were more likely to recover, and as proof, many of them still grace our landscapes today.
Basal sprouting or shoot generation on Live Oaks may be the response when the soil freezes and causes injuries to its roots. The tree will generate copious root shoots around its base, even when the root flare is visible.
Live Oaks and other Oak species- basically, all trees- Once we know a tree is viable, a root invigoration/fertilization program with biostimulants should be helpful. For injured trees, a countermeasure such as a wood-boring insect control may be helpful or even vital to the tree’s survival.
Your tree (like the Post Oak above) may need extra time to leaf out this year. The best thing you can do for your tree right now is to give them time to recover if they are able to do so.
Fruit trees- Variety-specific fruit trees may experience reduced yield. Plum and peach trees should recover. Fig trees may not be as fortunate; however, this tree is often able to regenerate stems from its roots.
Photinias, Chinese Tallow, Japanese Ligustrum- All these species had problems after the 1983 freeze, and I expect many will have problems again after the recent cold weather.
And, lastly, if you are wondering if you should do any post-freeze pruning, for the most part, pruning will not aggravate freeze injury. In fact, proper pruning may actually be helpful to your tree’s recovery and future growth.
For additional information on the effects of the February freeze on plant life, we recommend reading Neil Sperry's article on the subject: https://neilsperry.com/2021/04/just-a-little-bit-longer/.
Related more recent article on the February cold weather event's effect on trees: Tree's Damaged by February's Extreme Cold Weather.