Answer: Crape myrtle will grow under adverse soil conditions. It grows and flowers much better in well-prepared soil, however, so good soil preparation is well worth the effort involved. Preparation includes digging a large hole -- at least two times wider than the root ball. Set the plant in the hole no deeper than it originally grew in the container or field. Then backfill with the same soil removed from the hole after breaking apart clods and removing rocks or other debris. Research has shown that organic matter amendments are not necessary when planting in individual holes. Amendments in the hole encourage roots to stay within the hole and not grow outward into the surrounding native soil. Amendments are most beneficial, therefore, when they are incorporated uniformly throughout the soil surrounding the planting hole.
After planting, water thoroughly to settle the soil around the roots, and mulch to conserve moisture, reduce weeds and insulate the roots against extreme cold and heat. Three to five inches of pine straw, pine bark, shredded hardwood mulch or shredded leaves placed over the planting hole is ideal. Mulching a larger area beyond the planting hole is even better.
Water crape myrtle plants thoroughly at planting time and once a week, in the absence of rainfall, for the first two months after planting.
Established crape myrtle plants will tolerate drought. Flowering is enhanced, however, if plants are watered during dry periods that occur during the flowering season.
For strong growth and abundant flowering, plant crape myrtle in full sun. Heavy shade will reduce growth and flowering and will increase disease problems such as sooty mold on the foliage and powdery mildew on the flower buds and young growth. Large shade trees will also compete with the crape myrtle for moisture, causing poor growth and flowering. Lack of sunlight and moisture are the common causes of poor growth and flowering.
Crape myrtle flowers on new growth of the season, so you can prune plants any time during the late winter or early spring before growth begins without loss of flower buds. Avoid pruning in early fall before the first frost, because pruning forces new growth and keeps the plant from going dormant. Severe freezes can kill the plant if it is not fully dormant.
Pruning results in an abundance of new shoots that form flowers. It also reduces the amount of vegetative growth and funnels the energy of the plant into new growth and flowers.
On some cultivars, pruning to remove spent flower blossoms after they fade will stimulate new growth and another blossom flush in late summer. A second bloom is sometimes difficult to force on cultivars that bloom after mid-July.
In the case of your dwarf crape myrtles, prune the stems back to approximately 6 inches above ground level each year. Severe pruning will not kill or injure a healthy plant. Prune before growth begins in the spring. The result will be an abundance of new flowering shoots.
A complete general-purpose garden fertilizer -- such as 8-8-8, 10-10-10, 12-4-8 or 16-4-8 -- is ideal for crape myrtle. To newly planted small plants (1-gallon size), apply 1 teaspoon of fertilizer monthly from March to August along the perimeter of the planting hole. Larger, established plants will benefit from one broadcast application of fertilizer in spring. Apply 8-8-8 or 10-10-10 at a rate of 1 lb. per 100 sq. ft. or 12-4-8 or 16-4-8 at a rate of ? lb. per 100 sq. ft. Avoid over-fertilization because it causes excess growth and reduced flowering. The best time to fertilize is just before a rain. Otherwise, water in the fertilizer after application with irrigation. It is not necessary to remove mulch when fertilizing.
Hope this answers all your questions!
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