The number one question on my Sunday morning radio show is, "Why don't my hydrangeas bloom."
Most gardens are growing Hydrangea macrophylla, the mophead variety. They bloom on old wood. If you're out there pruning them at the end of the season, you're cutting off next year's flowers. Play it safe and don't prune the plant unless it's immediately after blooming. The other thing which might be happening is bud freeze out during the winter. I've been surrounding my plants with burlap and it's made them bloom like crazy.
In this segment for KDKA's Pittsburgh Today Live I look at other types of hydrangeas which bloom with ease in our climate.