Lack of Flowers on Hydrangea
You've covered almost all of the causes for poor hydrangeas blooms--improper pruning, late frost damage, and too much shade. The only other culprit I can think of is too much nitrogen, which would push your hydrangeas to produce leafy green growth and no blooms. High nitrogen is a possibility if you have applied turf fertilizer or bloodmeal near your hydrangeas. Nitrogen does flush down through the soil profile rapidly with regular rainfall, so if it is the problem, it should go away on its own. Try applying a high phosporous fertilizer lightly on the ground around your hydrangeas. Look for a fertilizer with a big middle number--10-30-10, for example. The phosphorous will push your plants to produce blooms.
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