Sunlight

• Crape myrtles require direct sunlight to produce flowers. The longer the plants are under direct sunlight, the better the chances they will bloom. If the crape myrtles have interrupted exposures to sunlight too often, they may experience diminished numbers of blooms that growing season. An added benefit to constant direct sunlight is that it heats up the soil surrounding the plants. This type of plant requires temperatures at around 80 degrees Fahrenheit in order to bloom properly. Shorter or cooler summers results in fewer crape myrtle blossoms.
  
  

Fertilization

• Crape myrtles require soil that has a low to average amount of nutrients. Too much fertilizer causes the plant to focus on growing taller and producing leaves instead of producing flowers. This is especially so for fertilizers high in nitrogen (the first number listed in the combination). If you use a lot of fertilizers in surrounding plants, trees or grass, it may seep into the soil around the crape myrtles and cause an unintended overflow of nutrients. A light application during the spring of 5-10-5 fertilizer is enough to give the plants nutrients but not so much as to limit the number of blooms.
  
  

Pruning

• Prune crape myrtles in late winter or early spring for the best results during the next growing season. Crape myrtles produce their blossoms on the new growth of the season. If you prune twigs and branches during the spring or summer months, you are removing this season's buds; fewer will bloom. Proper pruning of crape myrtles involves thinning the branches instead of a hard prune, according to Auburn University.
  
  

Environmental Stresses

• Crape myrtles experience a phenomenon known as environment stress when they receive too little or too much water or they encounter some sort of disease. While crape myrtles have a high tolerance for drought-like conditions once they become established, prior to that they can succumb very easily to drought. With too much rain, there is a possibility of the plants encountering fungal diseases, such as powdery mildew or root rot. Extreme stress on the plant could adversely affect flower production.