Every year about this time I get questions on how to dry hydrangeas....and no wonder, for their fat blossom clusters dry beautifully for wreaths, or just for a big vase of flowers once the garden has gone out of bloom. I've even been known to spray paint them with glitter or gold paint for the holidays...although they mellow to such lovely shades of plum, lavender and chartreuse the glitz really isn't necessary.
There are many ways to preserve their blossoms, but why not go the easy route? The trick is to wait until the blossoms dry part way on the bush; fresh blossoms don't dry well. Don't be too eager to pick them, especially after that biblical rain over the weekend. Hydrangea flowers, no matter which type, are ready to be dried when they've already turned a bit leathery on the bush.
I don't bother with powders or preservatives, nor do I hang them upside down. Just simply stick the cut stems into a vase with an inch or two of water, and let it evaporate. Don't crowd the heads, give them room for air to circulate. This method couldn't be simpler, and you get to enjoy the hydrangeas while they're drying.