Although summer sun takes a toll on many garden ornamentals in U.S. Department of Agriculture plant hardiness zones 7 through 9, crape myrtle shrubs and trees (Lagerstroemia spp.) need full sun to perform at their peak. These plants perform and look their best when the sun spotlights their deep-green summer foliage and cascades of brilliant white, lavender, pink, red or purple blooms. The amount of sun they get, however, is no more important than when they get it.
Defining Full Sun
More than one gardener has made the mistake of trying to grow crape myrtles in too much or too little sun. Understanding what full sun means -- and whether your planting site has it -- prevents a serious mistake. The University of Illinois Extension recommends that plants needing full sun should get at least six hours of direct sunlight each day. Whether they're continuous or interrupted doesn't matter, as long as the total number of hours is six or more.
Excessive Sun Problems
Crape myrtles planted in hot, dry climates do best with morning and late afternoon sun. From midday to mid-afternoon, they benefit from shade. If you live in such a climate, avoid sites with southern or western exposure; they receive the strongest, hottest afternoon light. Crape myrtles planted in these areas also suffer from the reflected light and heat of nearby light-colored structures or pavements. Sun-stressed plants frequently have dry, brown-edged, prematurely dropping leaves.
Inadequate Sun Problems
Crape myrtles receiving less than six hours of direct daily sun can't photosynthesize the food necessary for vigorous growth and flowering. Inadequate sunlight also exposes them to fungal infections. The University of Georgia College of Agriculture and Environmental Sciences cautions that sun-deprived crape myrtles have an increased risk of developing powdery mildew, a shade-loving, leaf-blemishing fungus. If your crape myrtle is hosting aphids, scales or other honeydew-producing insects, it is more likely to attract black sooty-mold fungus than plants in full sun.
Growing the Healthiest Crape Myrtles
As important as the right amount of sun is, crape myrtles won't do their best unless you meet their other cultural requirements. They need consistently moist, well-drained soil, are happiest in loamy clay and benefit from slow, deep watering during prolonged dry weather. For maximum flowering, feed them with a slow-release, high-nitrogen 16-4-8 fertilizer. In the first year after planting, apply 1 teaspoon of the fertilizer each month from March to August around the edges of the planting holes. After they’re established, scatter the fertilizer over the root zones in early spring at the rate of 1/2 pound per 100 square feet of soil and water it in. Don't overfeed because excessive nitrogen stimulates foliage at the expense of blooms.
- Fine Gardening: Lagerstroemia Indica
- University of Illinois Extension: Stepping Stones to Perennial Garden Design: Site Assessment -- Sunlight
- University of Georgia College of Agriculture and Environmental Sciences: Crape Myrtle Culture
- Arizona State University Extension: Lagerstroemia Indica
- University of Arizona Pima County Cooperative Extension: Lagerstroemia Indica
- Monrovia: Plant Selection
- North Dakota State University Extension Service: Questions on Crepe Myrtle
- Missouri Botanical Garden: Lagerstroemia Indica "Tuscarora"