Crepe myrtle (Lagerstroemia indica) is a popular flowering shrub and small tree known for its extended summer bloom period and attractive exfoliating bark. Achieving vibrant and abundant flowers requires proper fertilization, which maximizes bloom production and maintains the plant’s overall health. Providing the right blend of nutrients at the correct time ensures the plant focuses its energy on developing spectacular flower clusters.
Choosing the Right Fertilizer Blend
The NPK ratio of the fertilizer blend directly influences the crepe myrtle’s growth habit. A balanced formula, such as 8-8-8 or 10-10-10, is generally suitable, providing nitrogen (N) for foliage, phosphorus (P) for flowers and roots, and potassium (K) for general plant function. To boost bloom production, many growers prefer a blend slightly higher in phosphorus, as this nutrient is directly involved in flower development.
Fertilizers excessively high in nitrogen should be avoided, as this promotes vegetative growth resulting in a lush, green plant with fewer flowers. For established plants, a slow-release granular fertilizer is highly recommended over quick-release liquid formulations. The slow-release nature provides a steady supply of nutrients over several months, sustaining the plant without the risk of immediate root burn or sudden growth spurts.
Determining Optimal Application Timing
Correct timing ensures nutrients are available when the plant needs them most. The primary feeding period should occur in early spring, just as new leaves emerge from winter dormancy. This initial application supports the flush of new growth, which is necessary because the crepe myrtle blooms exclusively on new wood produced during the current season.
A second, lighter application may be beneficial in late spring or early summer, just before the first wave of flowers appears. It is necessary to stop all fertilization by late summer, generally no later than July or early August. Discontinuing feeding allows new growth to mature and “harden off” before the first frost, preventing cold damage during the winter.
Step-by-Step Application Technique
First, determine the correct amount of fertilizer by consulting the product label and assessing the plant’s size. For established trees, the amount is often calculated based on the canopy area or trunk diameter. Using a measuring cup to portion the exact dose ensures even feeding and prevents over-application.
Spread the granular fertilizer evenly across the soil surface, starting six to twelve inches away from the main trunk. The target area is the drip line—the imaginary circle beneath the outermost branches—where feeder roots are concentrated. Avoid clumping the product or letting it rest against the trunk, as high salt concentrations can severely burn the bark and roots.
The final step is to water the area thoroughly until the soil is saturated. This action dissolves the fertilizer salts and moves the nutrients down into the root zone so the plant can absorb them effectively.
Recognizing and Preventing Over-Fertilization
Applying too much fertilizer can be detrimental, causing “fertilizer burn” where high salt concentrations draw water out of the plant roots. A common sign of excess nitrogen is vigorous production of leaves and stems at the expense of flower buds, resulting in few or no blooms. Other visual cues include browning or yellowing of leaf tips, wilting leaves despite adequate watering, or a visible white crust of fertilizer salts on the soil surface.
Preventative measures start with performing a soil test before application to identify nutrient deficiencies and prevent unnecessary additions. Always follow product directions exactly, as guidelines deliver the correct nutrient dose for a given plant size. Established, healthy crepe myrtles require less frequent feeding than young specimens, sometimes needing only a single application in the spring.