Guidance from Stauffers of Kissel Hill garden center for growing crape myrtle in colder zones (e.g., zone 6B where Stauffers is located):
Winter protection: increase the mulch layer around the base of the plant to 4" to insulate the ground and roots from fluctuating temperatures.
"The most important care for crape myrtles is in early April while the plant is still dormant:
Move existing mulch away from trunk and stems, and apply Espoma Holly-tone following the recommended rate on the package for the size of the plant. Re-spread the mulch to cover the fertilizer at 2-3' depth.
To stimulate root activity and push the sap up in stems or trunks, apply Miracle-Gro solution at a rate of 4 scoops per 1 gallon of water. The amount you apply will vary from 1/2 gallon to 2 gallons, depending on the size of the plant. Apply 3 times at 7 day intervals."
