Nitrogen is the nutrient that grows leaves. Phosphorous helps plants grow flowers (the middle letter and number on the NPK ratio). But, keep in mind, that crapemyrtles require very little fertilizer. Give them sunlight, heat, and water every now and then and they do great. Another thing to think about is are you pruning your Moonlight Magic late spring/early summer and cutting off the flower buds. If you need to prune it, do it early spring when it is first showing signs of leafing out.
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