Growth Rate

• Sioux crape myrtle has a moderate growth rate when grown in USDA Hardiness Zones 7 through 9, according to the University of Florida IFAS Extension. In ideal growing conditions, a healthy crape myrtle may exceed this growth rate and experience up to several feet of growth in a single growing season. The growing season for Sioux crape myrtle begins in late spring and lasts until early fall.
  
  

Stimulating Growth

• Traditionally, gardeners harshly prune crape myrtle, even cutting back the trunk during the winter months. This often results in thin stems that distort the desired shape of the shrub. The United States National Arboretum recommends removing dead branches and cutting back living branches slightly to promote vigorous growth. Cold winters often damage crape myrtles, but the damage is not apparent until the tree begins to put on new growth in the spring. Pruning in late spring or early summer aids in identifying damaged branches.
  
  

Proper Growing Conditions

• For optimum growth, plant Sioux crape myrtle in rich, moist soil and full sun. An established crape myrtle tolerates dry and moist conditions and clay, sand and loam with pH conditions ranging from slightly alkaline to acidic. The ideal soil is a heavy loam to clay with a soil pH between 5.0 and 6.5, according to the United States National Arboretum.
  
  

Maintenance

• Older Sioux crape myrtles or those growing in poor soil benefit from a light application of 5-10-5 fertilizer in the spring to help stimulate growth. Water it, during dry periods, through the first two growing seasons in order to establish. The United States National Arboretum recommends that growers avoid watering or excessively fertilizing mature crape myrtles to prevent excessive vegetative growth and few flowers.