They are probably Macrophylla Hydrangeas and you are also probably in a zone 5 like me. They bloom on their old growth from the previous season. In zone 6 or lower the buds are damaged from either early fall or late spring frost. Also they are damaged from bad winter temperatures. Now they make Macrophylla Hydrangeas that bloom on new or old wood. The popular series are Endless Summer, Forever and Ever, and Let's Dance that bloom in the Northern areas. Also Smooth & Paniculata Hydrangeas only bloom on new wood and are good for your area also.

Also some people like myself that have older style of Macrophylla Hydrangeas refuse to give up and winter protect them. I double wrap them in Fall with burlap and stuff them full of leaves and remove towards the end of April when there is no more chance of frost. It works most years. Good Luck!