Answer: The most common reason for crepe myrtles (Lagerstroemia indica)to bloom less is a lack of vigorous new growth. The reasoning here is that the plants bloom on new wood of the season and if growing conditions are poor and they are stressed, they will also bloom less. Although drought tolerant and not too fussy in general, a plant grown in a season with good rainfall and a soil that is adeaquately supplied with nutrients will yield better blooms than a plant growing through a droughty summer in impoverished soil. Improper pruning will also reduce blooming. Any pruning should be done in the very early spring. Pruning later in the season will remove flowering wood for that year. If you cut the plant back very hard each spring, it will produce larger flowers but probably fewer of them in overall number. It is not strictly necessary to prune each spring except to remove any dead wood and crossing branches, and then perhaps to optimize shape. Finally, pests such as aphids or scale or a fungal disease could stress the plant and as a result slow its growth. If you suspect such a problem, you might want to check with your county extension and perhaps provide a sample for a definite specific identification of the problem and their suggestions as to how to control it. I hope this helps you trouble shoot.
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