Timing

• The best time in USDA zones 7 through 10 to plant crape myrtles is in the autumn. While container-raised plants may be planted any time of year when the soil is workable, autumn planting allows the roots to establish better. As the crape myrtle loses its leaves and enters dormancy, the roots do not need to sustain leaves and rather focus on growing into the cool, moist soil across the winter. Conversely, the U.S. National Arboretum suggests ideally planting crape myrtles in USDA zones 7 and 8 in late spring to midsummer when they're actively growing. Healthy, vigorously growing crape myrtles bloom better the first year after planting as long as they are not stressed by drought, planted too deeply, or sited in soggy ground or too much shade.
  
  

Evaluate the Site

• While at least two or three years should pass before making a final determination that a newly planted crape myrtle isn't flowering well, the site could affect the ease of flowering. Crape myrtles need a landscape location that basks in at least six hours of uninterrupted direct sunlight. Newly planted crape myrtle benefit from an evenly moist soil, too. Although crape myrtles are heat and drought tolerant, dry roots lead to abortion of leaves and young plants do not extend their stunted roots outward into equally dry soils. Sandy or other low-nutrient soils also may stunt crape myrtle establishment.
  
  

Flowering Insight

• Weak, struggling crape myrtles may not produce flowers well, but also over-maintained or "over-loved" plants falter, too. According to the U.S. National Arboretum, too much irrigation, over-fertilizing and lack of summertime heat and sunshine can inhibit, delay or prevent flower production.
  
  

Recommendations

• Allow your newly planted crape myrtle at least two years to grow and establish before evaluating if it truly is not flowering to expectations. To bolster establishment of newly planted crape myrtles, apply a light scattering of slow-release fertilizer, such as 5-10-5, in spring as the leaves appear. An optional second fertilization may be done two months later. Conserve soil moisture by placing a 3- to 4-inch layer of organic mulch over the soil to shade and cool the soil, and to prevent competitive weeds and nearby lawn turf. If after three or four years the crape myrtle still isn't blooming well, you need to relocate it to a better site.