Very healthy leaves but no flowers
It might be too early in the season for them to bloom?
Do they get enough sun? Mine have just started to bloom, depends on where you live. Did you cut them way back last year? That can effect whether they bloom this year.
Usually when hydrangea won't flower, it is because of something simple, like pruning. Prune hydrangeas only after they bloom in the summer and not in the fall. Old wood hydrangeas start developing their bloom buds for next year in August and September. If you don't prune your hydrangeas real soon, then it is better to wait until next year. Otherwise you won't have any blooms next spring.
Too much nitrogen gives leaf production and no blooms. Change your fertilizer and make sure Hydrangeas are sufficiently mulched and watered.