The Crepe Myrtle (Lagerstroemia indica) is a popular ornamental tree celebrated for its long, vibrant summer bloom season. This sun-loving species is valued for the striking colors of its flowers and its attractive, often exfoliating bark. Maximizing the duration and intensity of these flowers requires a thoughtful feeding regimen to support its extended flowering cycle.
When Crepe Myrtles Need Feeding
The timing of nutrient application is important, as it aligns feeding with the tree’s active growth periods. The first application should occur in late winter or early spring, just before new seasonal growth begins to emerge. This initial feeding provides the energy needed for the tree to break dormancy and develop strong new shoots, where the summer flowers will eventually form.
A second, lighter application can be beneficial in mid-summer, typically around July, to sustain the plant through its long blooming period. Fertilization must be stopped entirely by late summer or early fall, often around the beginning of September. Ceasing to feed allows the tree to naturally slow its growth and “harden off,” which prepares the wood for winter dormancy and protects it from cold damage.
Selecting the Ideal Fertilizer Formula
When selecting a formula, the nutrient composition, indicated by the N-P-K ratio, is the primary consideration. Most Crepe Myrtles benefit from a balanced, all-purpose fertilizer with a ratio like 8-8-8 or 10-10-10. Formulas slightly higher in nitrogen, such as 12-4-8 or 16-4-8, are also recommended for general health and vigorous growth.
A slow-release granular fertilizer is preferred for established trees, as it provides a steady supply of nutrients over several months. Liquid fertilizers, which offer immediate uptake, are better suited for container-grown specimens requiring more frequent, controlled feeding. Avoid fertilizers excessively high in nitrogen, such as those formulated for lawns, as this nutrient encourages lush, leafy growth at the expense of flower production.
Proper Application Techniques
The location of the fertilizer application is determined by the tree’s root structure. Fertilizer should be spread evenly across the soil surface around the tree’s drip line, the area directly beneath the outer edge of the canopy. This is where the majority of the tree’s fine feeder roots are located, allowing for optimal nutrient absorption.
Keep the granules or liquid fertilizer at least 6 to 12 inches away from the base of the trunk. Placing fertilizer too close to the trunk can lead to a concentration of salts that may damage the root collar. Immediately after application, the area must be thoroughly watered. This helps dissolve the fertilizer and carries the nutrients down into the root zone for uptake.
Addressing Poor Bloom and Nutrient Deficiencies
A common problem is a lack of flowers despite new foliage, often a sign of nitrogen over-fertilization or insufficient sunlight. If the tree is in full sun but producing excessive leaves, a temporary switch to a high-phosphorus “bloom-booster” formula, such as 10-50-10, can help redirect the plant’s energy toward flower bud development.
Chlorosis, a yellowing of the leaves, signals a micronutrient deficiency. If the youngest leaves turn pale yellow while the veins remain distinctly green, the tree is likely suffering from iron deficiency. This often occurs in alkaline soils where high pH makes iron unavailable to the roots.
Targeted treatment for iron deficiency involves applying a chelated iron product to the soil or using a ferrous sulfate foliar spray. If the yellowing is concentrated on the older, lower leaves, it may indicate a magnesium deficiency, which can be corrected with an application of Epsom salts (magnesium sulfate).