For those who prefer the faded color of dried hydrangeas commonly sold at florist shops and home decor stores, waiting until the end of summer to cut and dry the blooms is ideal. But because you want to retain the brightness of the color, you should cut them when the color is at its peak -- and do so in the morning. To dry hydrangeas, simply place in a vase without water and let nature take its course. There is no reason to hang them upside down, as some do, unless the stems are too weak to hold blossoms upright in the vase. This method is the easiest -- and least expensive -- but you should expect a bit of color fading.
To retain the brightest color, try drying the flowers in silica gel, which you can find at craft stores. Silica gel is not really a gel; it's those crystal granules that fill the little moisture-absorbing packets that come with shoes and electronics. Here's how to use it to preserve your flowers:
Add about an inch or two of silica gel to a plastic food-storage container. The size you use is determined by how many flowers you want to fit in there at once, taking care not to crowd them or their shape will become distorted. You also can use multiple containers, preserving one bloom in each.
Snip the stem down to about 2 inches, and place the flower upside-down atop the silica gel. Scoop some granules over the underside of petals, and then carefully add more granules until the container is about half full and the flower is completely covered.
Snap on the container lid and leave undisturbed for four days, then gingerly pour out the silica gel and remove the flower(s).
Use in wreaths and arrangements as they are; to display in a vase, tape dried stems onto the shortened stems with florist tape.