Hydrangeas not blooming? You may be able to help them out by doing the following:
Make Sure They Have Enough Sun
While hydrangeas don’t need full sun, they do need some sunlight. Are your non-bloomers in heavy shade? That may be the problem.
Most hydrangeas don’t like to be cut back severely. They set their buds in the fall, so if you are cutting old wood, you’re cutting away flower buds too.
Lavish Them With Compost
Poor nutrition can cause a lack of blooms. For the best results, add compost in the fall and again in the spring to encourage maximum summer blooming.