Texas gardeners are abuzz these days with questions about crape myrtles and the special care they may need as we head into late spring.
My reply when asked about these popular plants often goes in three directions — depending on the particulars of a garden situation — so I’ll explain each one.
Crape myrtles bloom on their new growth, and by now that new growth should be coming out feverishly.
Take advantage of recent rains and warm weather to apply an all-nitrogen fertilizer, 1 pound per cumulative inch of trunk diameter per plant. Specifically, that means that if you have a three-trunked crape myrtle, with each trunk about 1 inch in diameter, you should apply 3 pounds of an all-nitrogen lawn-type fertilizer around the plant and water it in deeply.
If your tree-form crape myrtle is growing vigorously yet still sending up sprouts from its roots, remove those that you don’t want.
Genetically, crape myrtles are shrubs. We are the ones who decided they could be trained and used as small trees. When that’s the case, at least for the first several years in your landscape, you’ll have to remove the unwanted suckers.
Also, if your crape myrtle has branches that are rubbing or otherwise overlapping, remove any that are not critical to its good looks. That’s a difficult thing to describe, but it will be fairly obvious when you come across it.
Repairing freeze damage
This past winter was cold for fairly long periods, but it didn’t get anywhere near record-low temperatures here. But whether it was because of the sustained cold or because we were coming out of a drought, our crape myrtles were hurt badly. I’ve seen many with no leaves at all (except for sprouts from their bases) and others that are lethargic about leafing back out.
The good news about this kind of dieback is that it’s not permanent. The root systems are still healthy and vigorous, and they’ll be able to push moisture and nutrients into the new sprouts that are already developing.
If you have a crape myrtle that died back all the way to the ground, remove the old trunks as close to the soil as you can, but try to avoid damaging the new basal shoots, as they’ll be your hope for a new plant.
Once the trunks are out of the way, save 12 or 15 of the straightest, most vigorous shoots and leave them in place. Remove the rest.
The plant will be rather bushy for the next several months, but by summer’s end, the regrowth will begin to turn woody. The new shoots won’t be so brittle by that point either, which will allow you to thin the numbers of stems to seven or eight.
It’s a good idea to put some type of protective stakes alongside them so they won’t snap off during the winter.
By next spring you’ll be ready to choose the final three or five stems to use as the main trunks of the regrown tree. A good rule of thumb is to choose the most vigorous and straightest ones, as these will grow back into tree forms very quickly, and you’ll be back in the race.
Incidentally, this is the technique I use to restore crape myrtles that have been barbarically topped. Since it’s very difficult to prune them enough to help them outgrow the scars of having been topped, it’s usually easier to force them to start over.
Crape myrtle scale
You may have heard of this ugly little pest. It has been in the Metroplex for about a decade. The immobile insects resemble large mealy bugs and line the plants’ stems and twigs. They look like small, gooey popcorn kernels, and if you press against them, they exude red fluid.
For several years, this particular scale went unnamed — even after samples were sent to scale specialists at the University of Florida and the Smithsonian Institution. However, it has now been determined that it came from the Far East and is specific to the genus Lagerstroemia (crape myrtles).
It’s not uncommon to spot another insect around the crape myrtle scales. In its immature form, it resembles a segmented pillbug, but it soon matures into a black ladybug with two orange-red spots on its back.
If you see these insects on your plant’s stems and twigs, remember that they are very much your friends. Black ladybugs can clean up most of a scale outbreak in just a few weeks.
There is a chance, of course, that you won’t be lucky enough to find the ladybugs. When left unchecked, the crape myrtle scales will begin to exude sticky honeydew secretions — basically processed plant sap, and the perfect substrate for black sooty mold. This fungus is disfiguring to leaves and stems, and many people worry about it. However, the real culprit remains the scale insects.
To prevent mold, you must prevent or cure the scales. Limited research done by Texas A&M has shown that Imidacloprid systemic insecticide, applied around the bases of the plants in early to mid-May, provides the best control of this pest.
That particular insecticide is widely available in retail garden centers, hardware stores and national chain stores. Remember to follow the label directions when using this. One treatment per year should be sufficient.
It may be a small comfort, but if you get behind the curve in terms of prevention efforts, crape myrtle scale is mainly aesthetic. It is unsightly, but it won’t kill your plants.
Neil Sperry publishes “Gardens Magazine” and hosts “Texas Gardening” from 8 to 10 a.m. Sunday on WBAP/820 AM. Reach him during those hours at 800-288-9227. Online: http://neilsperry.com.