Crepe Myrtles, botanically known as Lagerstroemia, are popular flowering trees in warmer climates, prized for their long-lasting summer blooms and attractive form. Crepe Myrtles are deciduous trees, meaning they shed their foliage annually. This natural process is an adaptation that allows the plant to survive colder temperatures and conserve energy during the non-growing season. Their widespread popularity across USDA hardiness zones 7 through 10 is due to their resilience and the year-round interest they provide, even when completely bare.
The Annual Cycle of Deciduous Leaf Drop
The seasonal leaf drop in Crepe Myrtles signals the onset of dormancy. This annual cycle is triggered primarily by decreasing daylight hours and falling temperatures in late autumn. The plant prepares for winter by shutting down energy-intensive systems, including ceasing photosynthesis.
Before the leaves drop, they often undergo a color transformation, shifting from green to vibrant shades of yellow, orange, and red. This change results from chlorophyll degradation, the green pigment that captures sunlight. As the tree reabsorbs nutrients from the chlorophyll, underlying carotenoid and anthocyanin pigments become exposed, creating the striking fall display.
Crepe Myrtles progressively shed their leaves from late fall through early winter. The precise timing depends on the local climate; trees in milder zones may retain leaves longer than those subjected to early frost. Once bare, the tree enters deep dormancy, a period of reduced metabolic activity. This seasonal loss protects the plant from cold stress and helps it store energy for spring growth.
Causes of Premature Leaf Shedding
Shedding leaves outside of late fall or early winter suggests the Crepe Myrtle is experiencing stress. This premature leaf shedding is often a defense mechanism triggered by environmental conditions or disease. Improper watering is a common culprit; both prolonged drought and overly saturated soil prompt the tree to drop leaves to reduce moisture loss and root stress.
Fungal diseases frequently cause early leaf loss, particularly in mid to late summer. Cercospora leaf spot causes dark spots on foliage, which then turns yellow before falling prematurely. Powdery mildew, appearing as a white coating on new growth, can also lead to leaf distortion and drop, though modern hybrid varieties are much more resistant to this issue.
Insect infestations, such as aphids, can also cause significant stress. Aphids secrete honeydew, a sugary substance that fosters the growth of sooty mold. This mold blocks sunlight, leading to leaf yellowing and subsequent drop.
Winter Appearance and Exfoliating Bark
Once the Crepe Myrtle is fully dormant and bare of leaves, its unique architectural structure and bark are revealed, providing visual interest throughout the winter. The branches and trunk often display an appealing, sinuous form, especially in mature specimens. This winter silhouette contrasts sharply with the soft texture of the summer foliage and blooms.
The most distinctive feature of the dormant Crepe Myrtle is its smooth, exfoliating bark, a characteristic that makes it a prized landscape tree. As the trunk expands, the older, outer layers of bark peel off in thin patches, a process known as exfoliation. This shedding exposes the fresh, contrasting inner bark, which is often mottled with varying shades of cream, warm beige, cinnamon, and rust-red. Cultivars like ‘Natchez’ are valued for this stunning winter bark display, turning the leafless tree into a focal point.
Essential Care During Dormancy
The dormant winter period is the optimal time to perform necessary maintenance, particularly pruning. Proper pruning should be done in late winter, before new growth begins in early spring, focusing on shaping the tree and removing dead or crossing branches. A common mistake, often called “Crepe Murder,” involves severely topping the main trunks, which leads to weak, unattractive growth and should be avoided.
For Crepe Myrtles planted in borderline hardiness zones, providing a layer of protection is advisable where extreme cold dips are possible. Applying a thick, insulating layer of mulch, such as pine bark nuggets or straw, around the base helps regulate soil temperature and protect the root system. Minimal watering is necessary since the plant is not actively growing, but a deep watering during prolonged dry spells prevents desiccation.