The crape myrtle (Lagerstroemia indica) is a popular ornamental shrub or small tree widely recognized for its vibrant, long-lasting blooms during the summer months. These plants are native to the sub-tropics and thrive in full sun and heat, making them a staple in warmer climates. To ensure the most spectacular display of flowers, proper care is necessary, and this includes strategically timing the delivery of nutrients. Fertilizer application is a method of maximizing flowering potential and maintaining the overall health of the tree, while also preventing excessive, non-flowering vegetative growth. Misapplied nutrients can actually diminish the plant’s visual appeal and potentially cause harm.
Understanding the Crape Myrtle Growth Cycle
Crape myrtles are deciduous, meaning they undergo a distinct annual cycle that dictates their nutritional demands. During the winter, the plant enters a period of dormancy, shedding its leaves and significantly slowing its metabolic processes. This resting phase conserves energy and allows the plant to withstand colder temperatures.
As temperatures rise in early spring, the plant transitions into a phase of rapid, active growth, often referred to as the spring flush. This is when the plant’s energy demand for nitrogen, which supports leaf and stem development, is at its peak. Since crape myrtles bloom exclusively on new wood, the quality and quantity of this initial spring growth directly impact the summer flower display.
The plant spends the late spring and summer months producing new shoots and then forming flower buds, which is a highly energy-intensive process. The summer months are characterized by continuous blooming, which requires a steady supply of nutrients, particularly phosphorus, to sustain the lengthy flowering period.
Optimal Timing for Fertilizer Application
The most effective fertilization strategy is timed to support the crape myrtle’s distinct energy-demand phases. The initial application should occur in early spring, just as the first signs of new growth appear on the branches. Applying fertilizer at this time provides the necessary nitrogen to fuel the spring flush, which produces the new stems that will bear the summer flowers.
For many established plants, a single application of a slow-release fertilizer in early spring is sufficient to carry them through the entire growing season. If soil is poor or maximum bloom is desired, a second, lighter application may be beneficial. If a second feeding is planned, it should be applied in late spring or early summer, typically around June.
A critical consideration is the timing of the final application, which must be completed by mid-to-late summer, usually no later than late July or early August. Fertilizing beyond this point encourages the plant to produce tender new growth that does not have time to harden before the first frost. This soft new tissue is highly susceptible to cold damage and can weaken the plant over the winter. Stopping fertilization in late summer forces the plant to naturally “harden off” and prepare for dormancy.
Selecting the Correct Nutrient Mix and Application Technique
The ideal fertilizer for a crape myrtle is a balanced, general-purpose formula, such as a blend with a 10-10-10 or 8-8-8 nitrogen-phosphorus-potassium (NPK) ratio. Nitrogen promotes foliage growth, but using a mix that is too high in nitrogen (like a lawn fertilizer) can lead to excessive leaf and stem production at the expense of flowers, a common issue known as “all leaves, no blooms.” A balanced ratio ensures that enough phosphorus is available to support the development of flower buds and a strong root system.
A slow-release granular product is often the preferred choice, as it provides a steady, consistent supply of nutrients over several months, minimizing the risk of over-fertilization or root burn. The fertilizer should be spread evenly across the soil surface, beginning a few inches from the trunk and extending out to the drip line. The majority of the plant’s feeder roots are located in this area, directly beneath the outer edge of the branches.
It is important to avoid placing granular fertilizer directly against the trunk, as this can cause severe chemical burn to the bark and surface roots. After the fertilizer is applied, it should be thoroughly watered into the soil to activate the nutrients and help the roots absorb them efficiently. Watering also helps prevent fertilizer burn, especially if the application is followed by a period of dry weather.
Tailoring Fertilizer Schedules for Plant Age
The needs of a young, newly planted crape myrtle differ significantly from those of an established, mature tree. Newly planted crape myrtles need to prioritize root development over rapid top growth in their first one to two years. For these young plants, a very light, more frequent feeding schedule is recommended, often applying a small amount of fertilizer monthly from spring through August.
This light, consistent approach helps the plant establish a robust root system without forcing excessive, weak shoot growth. For instance, only about one teaspoon of granular fertilizer per plant, applied around the perimeter of the planting hole monthly, is often enough during the first growing season. Focusing on this root establishment phase ensures the plant is structurally sound for long-term health.
In contrast, mature, well-established crape myrtles often require less frequent feeding. Many established trees thrive with just a single, annual application of a slow-release fertilizer in early spring. If a soil test indicates a healthy nutrient balance, or if the tree is already producing ample blooms and growth, feeding may not be necessary every year. Over-fertilizing a mature tree can lead to excessive foliage and fewer flowers, so it is always safer to err on the side of using too little rather than too much.