Remove leaves that will be under the water when the flowers are placed in the vase.
Fill a vase with room-temperature water.
Boil 2 to 3 cups of additional water in a medium saucepan.
Pour the boiling water into a tall container, and place the hydrangea's stems into it.
Remove the hydrangeas after 30 seconds in the boiling water, and plunge the stems into the room-temperature water.
Remove all leaves from the lower portion of each hydrangea flower. Leaves under the water rot and cause the flowers to wilt.
Cut 1/2 inch from the bottom of the hydrangea stem while holding it under running water.
Poke holes around the hydrangea stem, 1 inch from the bottom, with a small needle. This helps the stem absorb water.
Add a packet of flower freshener, available at nurseries, to the water in the vase and place the hydrangea in the vase.
Pull the flowers from the arrangement every three days. Cut another 1/2 inch off the bottom of the stems, under running water and at a 45-degree angle. Pour out the water in the vase, add fresh water and replace the flowers in the vase.