The optimal time to fertilize crape myrtles is in the early spring, right before new shoots sprout. Fertilizing ensures abundant blooms from summer to autumn.
In order to properly fertilize crape myrtle, an individual needs to know the soil's pH level. Crape myrtles prefer somewhat acidic soil at pH levels of 6 to 6.5. If the soil is substandard for myrtles, an 8-8-8 or 10-10-10 formula fertilizer is sufficient to encourage positive growth. Use 1/2 pound of fertilizer for every 100 square feet beneath the plant. Be careful not to over fertilize, as this encourages the production of foliage over blooms.