There are many environmental factors causing crape myrtles from blooming.
Crape myrtles are normally the last flowering trees to bloom from spring through summer.
A few factors detrimental to crepe myrtles include lack of sun, crowded branching, fertilizer quantities, insect populations, and poor drainage.
Crepe myrtles grow best in conditions with full sunlight and plenty of air circulation throughout the branches.
Check to see if your myrtle tree is planted in an area with little or no sunlight.
There may also be other trees that block significant amounts of sunlight for your tree.
A full grown crepe myrtle will need at least the same width of airspace as the height.
For example, a myrtle fifteen feet high should have fifteen to thirty feet of space for proper growth, water, and sunlight needs.
Late winter and early spring are the best times for pruning crepe myrtles.
You should remove the dead and weak branches while considering the shape and form of your tree.
Evenly spaced branching and strong limbs are good signs your tree has ample room for new shoots along with balanced growth habits.
Be careful about pruning branches all at once.
The best areas to prune yearly include dead branches and sear suckers.
These should be cut flush with the base branch.
Another factor that may cause little or no blooms includes fertilizer quantities.
A soil test should identify the amounts of nitrogen and phosphorous present within the garden area.
Too much nitrogen will produce healthy leaves and limbs, but stunts the growth of blooms.
A quick remedy is to apply bonemeal, which adds phosphorous to the soil and balances the soil pH.
Check for any insects and pests on your tree.
These may also cause the tree stress and further reduce the prospect for new bloom growth.
Trees may prefer a sea kelp spray to encourage new foliage and bloom development.
Sea kelp is known to add necessary trace elements and nutrients to unfortified soil.
Another culprit may be improper drainage.
Crepe myrtles prefer moderate watering, clay soils with additional amendments to balance soil pH, and removal of spent blooms (or dried out).
With the proper care and maintenance your crape myrtles should enjoy many seasons with lush blooms.