Hydrangeas are a good flower to dry indoors to enjoy in arrangements all year long. The simplest way to preserve them is by air drying. Leave them on the shrub until they start to feel papery dry, rustling to the touch, then cut them. Nature has really done the drying for you. Cutting is done before the flowers turn brown or become too brittle to use and long before the first frost. When gathering your blooms, keep in mind how you plan to use them and cut the stem length accordingly. I like to cut the stems long and then reduce to the size needed.