Crape Myrtles are easy to root, here's how to do it:
- Using the new growth from this season prune cuttings at about 5-7 inches in length. It's best if the diameter of the cutting is a half inch or less.
- Use a pot at least one gallon in size to root and grow your cuttings. Fill the pot with a professional potting mix or a 50/50 mix of sand and peat moss. Tamp the soil lightly.
- Dip the lower half of a cutting in rooting hormone powder. Poke a hole 2-3 inches deep in the middle of the soil at the top of the pot. If a multi trunk Crape Myrtle is desired poke 3-5 holes in a triangular pattern about 1-3 inches apart. Insert the cutting(s) to a depth of about 3 inches and then tamp the soil lightly around the cuttings.
- Avoid full direct sun until the cuttings have rooted. Place your newly planted cuttings in a spot that gets a little early morning sun or filtered sun. This being said direct sun is not required. Crape Myrtles can actually be rooted indoors.
- Water the new cuttings. Misting is best. Mist them until the soil is damp. Do not over water. Dampness is all the cuttings need.
- The cuttings should begin rooting within a week or so. Allow enough time for the roots to reach the side and bottom of the container showing a healthy amount of root development. The root system can be checked by turning the pot upside down. The plant should slide out exposing the root ball and the new root system. Wait at least 45 days to check the roots. 60 days is probably better.
- Once the root system has developed to a point where they will hold the soil intact, remove the plant from the pot. Find a sunny location in the landscape. Crape Myrtles love sun. The more sun the better. At least 8-10 hours of direct sun is best. Dig a hole at least twice the width and a little deeper than the root ball. Mix in soil amendment, as advised in your area, with the native soil. Place the plant in the hole leaving the top of the root ball level with the ground or slightly above. Back fill and tamp the soil lightly.
- Apply a granular slow release fertilizer to the top of the root ball and slightly outward from the root zone. Just a few pinches of fertilizer will do.
- Water in the new planting and then water as needed based on the amount of rainfall. Once established, Crape Myrtles are very drought tolerant and in most areas will only require watering through the first season. If the soil is sandy or extremely well drained, regular watering in the future may be required.
Source: Gardenality How To Question