If you prefer, you can simply hang your hydrangea blossoms upside down, by their stems. Because of their large size, this is best done with individual blossoms, rather than bunching them together. Air dried hydrangeas tend to be a bit more brittle than water dried blossoms, but still beautiful.
You can also use other common flower drying techniques, like silica gel and microwaving.
While it's not optimal, you can push the timing a bit and wait until your hydrangea blossoms have begun to pick up their autumn tones of burgundy, pink, green or blue. It’s not the ideal way to dry hydrangea flowers, but you'll get interesting tones and they will keep for quite awhile.
However you dry your hydrangeas, expect the color to last for about 1 year. After that, it will start to fade out.