Q. What is the best time to prune crepe myrtle and what are the basic guidelines on how to do it?
- ---Joe in Howell, NJ & Percy in Memphis, TN
- ---Ed in Oklahoma City
I didn't heed your advice to prune my crepe myrtles in the fall. What can I do now to produce flowers for this summer; or must I wait another season?
- ---Stephanie in Voorhees, NJ
A. After more than 20 years in this business, I've come to believe that it must be a common human condition to hear advice in reverse. SO many people send me emails or come up to me at speaking gigs and say "I know you told us to get our grass seed down early in the Spring" or "I know you told us to prune in the fall, but…" when, of course, I have been saying the exact opposite about both topics for decades.
Although many people seem to develop a dire urge to go on a pruning spree in the fall:
- it is never necessary; there is NO plant anywhere on this planet whose health or blooming is improved by fall pruning;
- it is often counter-productive; fall pruning limits or outright destroys the upcoming show on plants that bloom in the Spring, like azaleas, lilacs, forsythia and rhododendrons; And
- it is potentially damaging—perhaps even fatal—to any plant. Pruning stimulates growth; pruning a plant that's trying to go dormant for the winter forces it to grow instead, sapping the plant of energy it may desperately need to survive, and creating weak new growth that's extremely prone to winter injury.
However, I must here confess that I did say it was ok to cut crepe myrtle stems down to a "stub" on a show that aired many years back. I knew that the plants were summer bloomers, flowered on new growth and, like butterfly bush, could survive a hard pruning…
Then a legion of extension agents around the country wrote and called to implore me to retract this advice and instead beg people not to commit what they had come to call "crepe murder", explaining that while the practice did seem to fill the need that many gardeners have for committing acts of over-the-top operatic horticultural violence, it made for a pretty sad plant after a while—unless you like the look of spindly shoots rising out of elephant-sized legs.The time to prune a crepe myrtle is late winter through early Spring, with the most sound advice being to wait until the plant begins to put out its first new growth of the season, but not much longer. And while whacking the poor thing back to the ground isn't advised, some pruning is. Virtually everyone agrees that a little haircut in early Spring will induce a crepe myrtle to produce more flowers that summer.
So that's the basic answer: a little trim to remove the tips of branches is all you'd want to do on a tree or shrub that has a nice pleasing shape and hasn't outgrown its spot. And the further North crepe myrtles are grown, the more these Southern favorites are also going to suffer a little inevitable winter injury—especially after the kind of slap-you-silly winter many of us just had—so any damaged portions should also be removed.
Now we get to optional pruning, personal choice and whether or not you bought the crepe myrtle you should have. The original form of the plant—a deciduous tree originally from Asia—grows naturally to 25 or 30 feet tall and develops a very open shape when left unpruned. There are also dwarf varieties that top out at a very tidy six to eight feet, semi-dwarfs that are about twice that tall, and new 'minis' that are said to stay very small and shrub-like without much pruning.
Unless you have no choice (i.e., you planted or inherited a standard size tree that has dramatically outgrown its space), the best pruning keeps a fairly natural shape to the plant while following the basic rules for woody plants: Completely remove some of the oldest wood by cutting it back low, remove branches that are crossing or rubbing against each other, and maybe take some out of the center to improve airflow—especially if the plant is in a crowded spot or it's become a tangled mess.
Again, the natural habit for most crepe myrtles is to have a fairly shrubby appearance and shape, but some people want to make them look more like their idea of a true tree. In his classic garden tome, "The Pruning Book" (published by Taunton Press) our old friend Lee Reich describes a multi-year process that involves careful pruning out of smaller, secondary branches to gradually reveal a single trunk that achieves this goal.
Whatever you choose to do, always try and follow the 1/3 rule—don't remove more than one-third of the growth in any one season. If you want to dramatically reshape a crepe, do it over the course of several seasons. Oh, and don't be a crepe murderer! (Or if you DO, please don't say I told you to!)