Pour 1 cup of water into a pot and place on medium heat on the stove. Bring the water to a boil. While you are waiting for the water to boil, you can complete Step 2.
Remove the hydrangeas from their current vase. Using your garden shears, cut off about an inch of the stem at an angle.
Pour room temperature water into a vase. This will be the vase into which you put the revived hydrangeas. If the hydrangeas are a part of a larger arrangement, then you can go ahead and put the other flowers into the vase and add the revived hydrangeas later.
Add floral preservative to the water and stir to combine, if desired. If you bought your hydrangeas at a florist, they may have come with a pack of powdered floral preservative. You can also buy some from a gardening store or nursery. This step is optional, but floral preservative can help cut flowers last longer.
Pour the boiling water into the cup. Place the cut hydrangeas into the boiling water. Wait 30 seconds, then switch them over to the room temperature vase.
Arrange the flowers as you normally would. This procedure should revive limp or drooping hydrangeas. It could take up to a few hours to see the difference, so be patient.