The Crepe Myrtle, Lagerstroemia indica, is a popular flowering tree and shrub known for its vibrant, long-lasting summer blooms. To maximize the health and flowering potential of this species, providing the correct nutrients is necessary for optimal growth. Applying the wrong kind or amount of fertilizer can hinder the plant’s ability to produce flowers, making a targeted feeding strategy important.
Recommended Fertilizer Formulas
Crepe Myrtles generally perform best with a balanced fertilizer or one with a slightly higher potassium (K) content. Look for formulations where the Nitrogen (N), Phosphorus (P), and Potassium (K) numbers are equal, such as 8-8-8 or 10-10-10. A slow-release granular fertilizer with a 3-1-1 ratio, like 18-6-6, is also highly effective as it provides a steady supply of nutrients over several months. Selecting a formula designed for flowering trees helps promote bloom production rather than just excessive leaf growth.
Avoiding high-nitrogen formulas is important, as excessive nitrogen encourages lush green foliage at the expense of flower bud development. Too much nitrogen can lead to a condition where the tree looks healthy but produces few blooms. Established trees in nutrient-rich soil often need less fertilizer than those in poor or sandy soil.
Beyond the primary NPK macronutrients, Crepe Myrtles sometimes require secondary nutrients to correct specific deficiencies. Chlorosis, which appears as yellowing leaves with green veins, indicates a potential lack of iron or magnesium. Applying a fertilizer fortified with micronutrients like iron, manganese, and sulfur can help restore the deep green color to the foliage.
Proper Timing and Frequency
The most effective time to begin fertilizing established Crepe Myrtles is in early spring, just before new growth begins to emerge. This application provides the necessary energy for the plant to start its active growing cycle. For most homeowners, a single application of a slow-release granular fertilizer at this time is sufficient for the entire season.
If you are using a standard, non-slow-release granular fertilizer, a second, lighter application may be beneficial in early summer. This mid-season boost can help support the plant during its heavy flowering period. For newly planted trees, a light monthly feeding throughout the first growing season helps establish a robust root system.
It is important to stop all fertilization by mid-summer, typically no later than late July or early August. Ceasing fertilizer applications allows the plant to naturally slow its growth and “harden off” before the onset of cold weather. Fertilizing too late in the season can encourage tender new growth that is highly susceptible to winter damage.
Application Techniques
When applying granular fertilizer, the goal is to distribute the product evenly over the root zone, which extends out to the tree’s drip line (the area beneath the outer edge of the canopy). Broadcast the fertilizer uniformly across this area to ensure the feeding roots can absorb the nutrients.
Care must be taken to avoid placing the fertilizer directly against the trunk of the tree. Keeping the granular product clear of the main stem, typically by at least five inches, helps prevent stem burn. If you are using a liquid fertilizer, mix it according to the label directions and apply it evenly over the root zone with a hose-end sprayer.
After applying any granular fertilizer, thoroughly watering the area is a necessary step. This watering action helps dissolve the fertilizer granules, allowing the nutrients to move down into the soil where the roots can access them. It also helps prevent the fertilizer salts from drawing moisture out of the roots, which can cause burn damage.
Recognizing and Preventing Over-Fertilization
A common sign of over-fertilization, especially with high-nitrogen products, is the development of many leaves but very few flowers. Another consequence of excessive fertilizer use is visible fertilizer burn, which occurs when too many salts accumulate in the soil.
Symptoms of fertilizer burn include the browning and crisping of leaf tips and edges, along with general leaf yellowing and wilting. In severe cases, a white or crusty layer of salt deposits may become visible on the soil surface around the tree. This salt buildup can actually reverse the osmotic pressure, causing water to flow out of the roots rather than into the plant.
The most effective prevention is to always follow the application rates listed on the fertilizer product label. It is always safer to apply slightly less fertilizer than the recommended amount, as it is difficult to remove excess nutrients once they are in the soil. Consistent, deep watering after application will also help flush any concentrated salts away from the sensitive root zone.