Will regrowth start on your landscape plants?
This was an unprecedented weather event, so no one really knows how bad the impact on plant materials will be. This also was a unique event because we were below freezing for so long, and for part of that time did not have snow cover to insulate plants. It doesn’t appear that soil temperatures got too low, so hopefully we won’t see a lot of winter injury to plant roots, but only time will tell.
Flower buds, vegetative buds, branches, stems, crowns, bark, roots or even whole plants may be injured by winter extremes. Containerized plantings are particularly vulnerable to low winter temperatures since their roots are not protected by being below ground.
Oklahoma City lies in the U.S. Department of Agriculture Plant Hardiness Zone Map in Zone 7a. Plants frequently injured by low winter temperatures are those planted in areas north of their appropriate hardiness zone. Marginally hardy plants, such as Zone 8 species, will suffer.
However, even hardy plants can be injured during unusually cold temperatures. This is especially true if the plants have not been managed properly with fertilization, pruning and irrigation.
You can lightly scratch the thin bark of a young stem with your fingernail, and if the inner bark is still green, it should still be able to survive. But, just checking bark for “green” is not enough as roots on many plants may resprout from the base.
There are many plants that have obvious damage, but it is very likely most will leaf out this spring, even some of the broadleaf evergreens. Later in the spring, if you do not see new growth at the tips of stems, look for new growth lower down on the stem or from the base, but be patient as regrowth sometimes comes out later than the normal spring bud break.
We have had many inquiries about Yaupons and other hollies and several other broadleaf evergreens. Plants may have dead leaves and appear to be dead, and they could possibly lose every leaf they have, but if the wood is good, the buds should be alive, and the plant can re-leaf.
We also have received numerous calls concerning Deodar Cedar, Live Oak and Magnolia trees. Deodar Cedars are a Zone 7b tree, which is marginal for here. Live Oaks are another tree that we are growing on its northern limits as a Zone 7 tree. Again, it is best to wait and see if the limbs bud and leaf out.
And what about the crape myrtles? We would expect that most will have died back to the ground with these temperatures, but no one knows for sure yet. Again, wait to see before drastically pruning.
My recommendation is to be patient until spring growth truly arrives and new plant growth starts, to see how much die-back has occurred and what portion of the limbs will bud back out before making decisions on hard pruning or plant removal.
You could do a fertilization in mid to late March to give trees and shrubs a boost. Consult OSU Fact Sheet No. 6412, “Fertilizing Shade and Ornamental Trees and Shrubs,” which you can find at osufacts.okstate.edu.
Julia Laughlin is an extension educator in horticulture with the Oklahoma State University Cooperative Extension Service in Oklahoma County. Email her at firstname.lastname@example.org.