We are getting a lot of questions about this topic, and it also seems like every other post in social media garden sites are asking what to do about their crapemyrtles. So, let’s talk about our frozen crapemyrtles.
First of all, we love our crapemyrtles and for good reason. They are durable, they grow fast, and you get flowers. This is why you see so many of the shrubs in northeast Oklahoma. But here is the rub. The upper limit of appropriate growing zones for crapemyrtles is Zone 7. We are essentially in Zone 7 so we should be good… right? Not necessarily.
Growing zones or cold hardiness zones are established by the USDA. Growing Zone 7 means that our winter lows “on average” don’t get below 0 to 5 degrees. Well, that went out the window during our deep freeze when we experienced Growing Zone 5 winter conditions: -15 to -20 degrees. And therein we see the problem. Our crapemyrtles were not built for the record lows we experienced, and this is why a lot of them are looking terrible right now.
We have a couple of crapemyrtles in our landscape, and they look fine, but as I walk around the neighborhood or drive around town, this is not everyone’s story. There are some large, neighborhood crapemyrtles that have not leafed out yet and that doesn’t bode well for their future.
At the OSU Extension here in Tulsa we have been telling people to “wait and see” for several weeks but the question is: how long do we wait?
To better answer this questions Brian Jervis (OSU Extension Horticulturist/Tulsa) and I decided to reach out to one of the foremost experts of crapemyrtles we know: Dr. Carl Whitcomb. Dr. Whitcomb is a retired professor from OSU and a long-time researcher who now concentrates most of his efforts at his Lacebark Research facility located just outside of Stillwater.
Dr. Whitcomb gave us some general rules for assessing our plants after the freeze. He told us that most landscape plants such as oaks, elm, ash, maple, and other trees as well as lilacs, spiraea, and weigela should be fine since they have some degree of cold tolerance. However, other marginally cold tolerant species such as crapemyrtles, nandina, photinia, and some hollies likely have some dead wood.
Many people have suggested that to determine if your shrub is still alive, you should scrape the bark to see if any there is any green under the bark. Dr. Whitcomb told us, “The green under the bark remains because the roots were not damaged and are still moving water up through the dead cells of the xylem, thus protecting the damaged phloem cells (outer bark) from dehydrating.” Because of this, Dr. Whitcomb said scraping the bark to look for green is not a reliable way to determine plant health.
He told us that he and his students had previously completed research to help determine the critical temperature at which we could expect to see damage to our crapemyrtles. Their research showed that even somewhat tender species like crapemyrtles, hollies, and nandinas were relatively fine down to 5 degrees. But once the temperature dipped below -5 degrees, the tops of the plants were dead and new growth could only be seen later as it emerged from the soil level crown of the plant. Further research revealed that -2 to -3 degrees seemed to be the threshold beyond which there would be permanent damage.
During our deep freeze, temperatures got down in the -15 range, so you can see why there are so many struggling crapemyrtles all over town.
Everyone wants to know what they should do about their crapemyrtles. Dr. Whitcomb suggested we continue to wait until mid-June before we start cutting and pruning our crapemyrtles. He told us, “Cutting off tops now offers no advantage over cutting what may be for–sure dead tops later.”
While the branches of many crapemyrtles do indeed look dead, he said they will likely start shooting up new shoots from the crown and there might be quite a few of these shoots. He suggests that we then “begin selective pruning out the ‘extras’ and saving the strongest ones to get back to the best 4 or 5 stems.” This is of course if this is the look you prefer for you crapemyrtle.
The deep freeze was pretty devastating for many of our crapemyrtle plants. But it sounds like many of them will start putting out new shoots (if they haven’t already) even though the large stems might be dead.
So, your best bet is to continue to wait until mid-June before doing any drastic pruning on your crapemyrtles. After that, it will be time to either let them re-grow from the crown of the plant or think about replacing them with a larger plant. As for me, I am a big fan of letting them re-grow. Special thanks to Brian Jervis for connecting us with Dr. Whitcomb.
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You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th St., or by emailing us at email@example.com.