By this point in January many homeowners note that some of the neighbors have cut their crepe myrtles severely, while others have only snipped back the branches. Still others haven’t pruned at all. Even more confusing, the crepe myrtles seem to bloom about the same regardless. How to decide what to do depends on the age and condition of the trees. And no, it’s not too late if you opt to chop, snip, or clip.
If you move in where crepe myrtles have grown for years, they may be 30 feet tall with few blooms. Because they are old and obviously unpruned for ages, let them be or call in an arborist to thin the branches and tip them to stimulate possible new flowers. A true pro will shorten branches on such a ‘grand dame’ specimen to the point where they are about the size of your thumb and no more. This ‘thumb’ approach also works well for somewhat shorter trees whose branches look smooth all the way to their ends. At the other end of the spectrum, your crepe myrtles may be 12 feet tall and have swollen ‘knobs’ at the top of each trunk. These knobs characteristically sport lots of small stems extending in all directions and indicate a severe pruning regime. Such crepe myrtles have been pruned each winter to control their height and produce lots of flowering stems. It’s a good idea to continue the practice for these trees, or prepare to look the other way as you coax them to grow out of their established pattern.
Change the rules
To alter the way a knobbed crepe myrtle grows can take two or three seasons, but even then some flowers will manage to bloom. Some gardeners cut off the trunks entirely right below the gnarly knobs, then select new branches from the numerous sprouts that emerge. Others leave the knobs and choose 3 from among the existing stems to encourage, then prune the rest away completely. Keep nitrogen fertilizers to a minimum, and consider root feeding with phosphorus and potassium to build strong new branching and discourage watersprouts at the base or from the knobs.