There are a number of possible explanations for why your hydrangeas may not be producing blooms. The most likely culprit is injury over the winter. But it could also be that they are not in an ideal location in your garden. They might not be receiving enough sunlight, or the soil might not be rich enough. If that is the case, adding compost and/or moving the hydrangeas might help. Sometimes hydrangeas also fail to bloom if they are receiving excess nitrogen.