Fill the display vase with 110 degree Fahrenheit water. Mix a flower preservative powder, available from florists, into the water.
Strip the leaves off the hydrangea stem. Hold the bottom of the stem under water and cut off the bottom inch at 45-degree angle.
Place the hydrangea stem in the prepared vase. Add water until the entire stem is submerged and only the flowers sit above the water.
Mist the hydrangea flower with warm water from a spray bottle. The added moisture prevents the flower from drying out before it begins absorbing water from the vase.
Display the hydrangeas in a cool room where they receive bright but indirect sunlight. Replace the water when it discolors or every one to two days.