Crepe Myrtles (Lagerstroemia indica) are popular ornamental shrubs and small trees in warm climates, cherished for their long season of vibrant summer blooms. These deciduous plants are relatively low-maintenance, but their spectacular flowering performance depends on receiving the right nutrients at the correct time. Providing the proper fertilizer maximizes flower production, ensures healthy foliage, and supports the plant’s overall vigor and disease resistance. Understanding the correct nutrient balance and application schedule is fundamental to cultivating a thriving, heavily-flowering Crepe Myrtle.
Selecting the Ideal N-P-K Ratio and Fertilizer Type
The most effective fertilizer for Crepe Myrtles is a balanced formula supplying equal parts of the three primary nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K). Standard ratios like 10-10-10 or 8-8-8 are suitable for established plants in most garden soils. Nitrogen promotes leafy growth, Phosphorus supports robust root development and flower production, and Potassium contributes to overall plant health and resilience.
Some experts recommend a formula slightly higher in Nitrogen, such as 12-4-8 or 18-6-6, especially for younger trees to encourage canopy growth. Conversely, if a mature tree produces ample foliage but few flowers, a high-phosphorus “bloom booster” formula, such as 10-15-9, can be temporarily used to encourage heavier blooming. Granular, slow-release fertilizers are the preferred application method for Crepe Myrtles.
A slow-release product, often consisting of coated granules, releases nutrients gradually over several months, providing sustained feeding that matches the plant’s long growing season. This method is safer and more convenient than quick-release water-soluble liquids, which require frequent application and carry a higher risk of damaging the roots. The sustained delivery of nutrients from a slow-release formula promotes steady growth and helps prevent the sudden flushes of tender new growth that can attract pests and diseases.
Essential Timing and Frequency for Application
The correct timing of fertilization is as important as the product you choose, influencing the quantity and quality of summer blooms. The primary application window for Crepe Myrtles is in the early spring, just before the first flush of new growth begins. This timing ensures the plant has immediate access to nutrients as it breaks dormancy, fueling the development of the stems that will support summer flowers.
For established trees, a single application of a slow-release granular fertilizer in spring is sufficient for the entire growing season. If the plant is large, in poor soil, or is a heavy-feeding cultivar, a second, lighter application can be made in mid-summer, typically around July. This mid-season boost helps sustain the plant through the peak flowering period, which can last for several months.
Fertilization must stop by late summer or early fall, usually around Labor Day. Ceasing nutrient application allows the plant to naturally slow its growth and begin the process of “hardening off” its tissues. New growth stimulated by fertilizer late in the season will be tender and highly susceptible to damage from an early frost, compromising the plant’s ability to survive the winter.
Preventing Over-Fertilization and Common Issues
Applying too much fertilizer, especially one high in nitrogen, is a common error that leads to the “all leaves, no blooms” problem. Excessive nitrogen promotes vegetative growth, resulting in a tall, leafy tree that produces very few flowers. Over-fertilization can also cause “fertilizer burn,” which appears as brown or yellow leaf edges and a visible crust of salt on the soil surface.
When applying granular fertilizer, distribute the product evenly across the root zone beneath the tree’s canopy, extending out to the drip line. Keep the fertilizer granules several inches away from the trunk and main stems to prevent direct chemical burn to the bark and root crown. After application, the fertilizer must be watered in thoroughly to move the nutrients into the soil where they can be absorbed by the roots.
A significant concern related to over-fertilization is the exacerbation of Crepe Myrtle Bark Scale (CMBS), an invasive pest. Excessive nitrogen encourages the production of soft, tender new growth, which is highly attractive to the scale insects. By using a slow-release, balanced fertilizer and avoiding over-application, growers can maintain plant health without unintentionally creating an environment that encourages pest infestations.