Not long ago, I received the following email: “I have two crape myrtle trees in my front yard, one about 25 years old and one about 10 years old. They are in full sun. They usually bloom later than other similar trees in our neighborhood, but five years ago, neither one had a single blossom. The following year, they bloomed as usual, then the next year, nothing. Last year, they had lots of flowers, but this year, nary a one. The older tree was pruned three years ago in the winter but other than that, all other variables except the weather have remained constant. When there are flowers, they are pale pink. Your thoughts?” – Karen Burkland, Sherman Oaks
My first thought was that trees had grown up over the crape myrtles in question and taken away their light. In truth, crape myrtles can bloom in partial sun, even if flowering at their maximum potential will necessitate 6-8 hours a day of full sun exposure. Upon clarifying that there were no overhanging trees, I asked about the watering regimen and learned that the trees were watered everyday. This likely explains the trees’ lack of flowering.
Crape myrtle (Lagerstroemia indica) is native to the monsoon climate of Southeast Asia, where the dry season can extend from 3-6 months. It then stands to reason why soil kept moist could inhibit flowering; a dry season is an essential element of the trees’ ecosystem.
Although there are many crape myrtle hybrids, wild crape myrtle trees flower in the pink to red spectrum, so the pink-flowered specimens in Sherman Oaks would be closer to the wild types and thus more sensitive to constant soil moisture.
In general, why should moist soil be a problem for plants if water is so crucial to their growth? The problem is that standing water in the soil deprives roots of oxygen. Just as we cannot keep our heads underwater for very long due to oxygen deprivation, roots that stand in water (speaking of land plants) can suffocate, too. Excess water in the root zone is also an invitation to pathogenic organisms, especially water molds, Phytophthora notable among them. Even in borderline situations where excess moisture is not killing the roots, their capacity can be adversely affected as they fail to take up minerals needed for metabolic functions such as flower bud formation. Hormonal activity in trees, including that related to flower bud formation, is also negatively impacted by poor root health
Due to crape myrtle’s sensitivity to powdery mildew foliar fungus, hybrid varieties resistant to this fungus have been developed. These varieties have the names of Indigenous tribes such as Muskogee and Zuni (purple flowers), Lipan (lavender flowers), and Natchez (white flowers with deep cinnamon bark). Otherwise, crape myrtles are generally considered pest- and disease-free. However, there is an aphid species that singles out crape myrtle as a host, and this, ironically enough, has proven to be a boon to pecan growers. Since this aphid attracts a wide variety of beneficial insects that prey on it and pecan pests, crape myrtles have been planted in pecan orchards with a positive impact on pecan harvests.
The fact that the Sherman Oaks crape myrtles were winter-pruned could not have had any effect on flowering since crape myrtles are among those trees whose flower buds are formed in spring or even later in the growing season. No matter how radically these trees are cut back in winter, they will put on new shoot growth followed by a flower show in spring or summer, albeit later than normal when the pruning is severe. Jacaranda is one such tree. Not only does its flower bud formation coincide with the crape myrtle’s, but it also blooms more heavily following a dry winter. This is also true of floss silk tree (Ceiba species), which shares jacaranda’s South American habitat. It prefers a dry winter for summer flower bud formation. You can see it blooming now with its large star-shaped orchid-pink flowers that will persist through the fall. The floss silk tree is also distinguished by a thorny, succulent trunk whose bark is green when it is young. A century ago, the silky fluff found in its football-size seed capsules was used for stuffing car seat upholstery.
Incidentally, crape myrtle trees self-sow when the soil is to their liking. I have several volunteer crape myrtle trees that grew up in that fashion. Not long ago, Barbara Starr, who gardens in the San Fernando Valley, sent me a picture of dozens of seedlings that were growing adjacent to her back wall. They looked like crape myrtle seedlings and, sure enough, her neighbor had a crape myrtle growing on the other side of the wall that was responsible for those many volunteers that she found highly attractive. Their stems and new growth are wine-colored and do present a fresh and cheery look.
Before leaving crape myrtles, we should spend a moment clarifying where the “a” in crape myrtle comes from, since the tree is named for its flowers’ texture, which is reminiscent of crepe, a crinkled and ruffled fabric. ”Crape” is merely the Anglicized version of “crepe.” It transpires, however, that when this tree is written about in the Southeastern US, where its explosive flower show easily eclipses that seen in Southern California, both “crepe” and “crape” are used interchangeably when discussing this tree. There is no botanical relationship between crape myrtle trees and myrtle shrubs, but they do have smooth, exfoliating bark in common. Last but not least, I should mention that crape myrtle leaves turn gold and red and burgundy before dropping in the fall.
California Native of the Week: The island or dune wallflower (Erysimum insulare) is a rare, short-lived perennial growing two feet tall and one foot wide. It bears yellow flowers that will remind you of those of Bowles Mauve, a popular wallflower in the nursery trade that blooms heavily until it exhausts itself from overly abundant flower production and dies. The island wallflower stabilizes sand dunes and bluffs along the California coast and on the Channel Islands. It loses its leaves when stressed but is hardy to 20 degrees. Remove spent flowers and new growth will emerge from its base. If anyone knows of a source for this plant, please advise.
Do you have crape myrtle tale to tell or just a favorite tree you think more people should know about? If so, you are invited to send it to joshua@perfectplants.com. Your questions and comments, as well as gardening conundrums and successes, are always welcome.
