I know of two basic methods for drying big head hydrangeas (this will include mophead hydrangeas (macrophylla) and also the paniculata hydrangeas (Limelight, PeeGee, Pink Diamond, Tardiva, etc) as well as the Annabelle type hydrangeas (arborescens). I know there are more than two methods but these are the simplest ones in my opinion. In the first method I cut several blooms from the shrub when the blooms were mature. That is, they were just passing their prime and beginning to dry. I placed the bouquet in a vase with about 1-2" of water. Over a period of about one week the blooms dried on their own.
In the second method I left the blooms on the shrub to dry naturally. Just prior to the blooms turning brown is when I cut the blooms. These can be placed directly in a vase with no water. Nothing more needs to be done to have these hydrangeas preserved.
I sometimes paint my blooms. Michael's Hobby Store sells a mist aerosol paint specially made for blooms. It is a very fine paint and will not weigh down the flowers. This paint works great and comes in a wide variety of colors. You might also spray the flowers with hairspray if you don't want to color the blooms. The hairspray will help the petals hold up a bit longer.
Flowers dried in this way can last for many years but do tend to get covered with dust. It is difficult to dust dried flowers so I usually throw my old flowers out. One thing to note, if you are into feng shui you do not want dried flowers in your house at all. I tread a fine line because I do like feng shui and try to practice it, but I also love my hydrangeas in the house as well. My compromise is to not have as many dried flowers as I'd like and to toss them in the spring. Your choice for sure.
I know this is an easy question, but which hydrangea was dried in water and which one was dried on the shrub in the above picture? The green or the white? And can you see the oakleaf hydrangeas outside the window? They dried naturally on the shrub. I'll enjoy those blooms from inside the house when it is icy outside.
in the garden....