To dry hydrangeas all you have to do is cut the blossoms with about a 5-6 inch stem when they start to feel a tad “papery”. Strip off all the leaves and place into a vase of water. Allow the blossoms to suck up the water slowly and then add more water as needed until the blossoms are completely dry. This will take a few weeks, so be patient. Be sure to keep them out of direct sunlight also.