Place the freshly cut flowers in a vase with fresh water. Make sure the stems are at least half covered with water.
Move the vase to a cool spot, out of direct sunlight. The flowers will still look attractive, so go ahead and display them.
Don’t add more water as the water in the vase evaporates. It’s just there to allow your hydrangeas to dry naturally, rather than simply dry out. Once the water is totally evaporated, your hydrangeas should feel dry to the touch and ready to use.