Fill a bucket with warm water. The temperature should be about 100 to 110 degrees Fahrenheit.
Add a floral preservative to the water. Use a commercial preservative. They contain ingredients to encourage buds to open and prevent bacteria growth, according to Texas A&M University System's Aggie Horticulture website.
Harvest the flowers. Clip the stems at an angle, and immediately place them in the bucket of water. An angled cut allows the flower to absorb more water than a horizontal cut.
Strip foliage that will be below the surface of the water from the stems. Submerged foliage will rot and taint the water with bacteria or fungi growth, which can clog the stems.
Place the bucket in a cool location for about an hour to let the flowers harden. During this time, the warm water will move rapidly up and through the flowers. In fact, the flower will take up almost as much water during this one hour as it would in its entire life in the ground, according to the University of Minnesota Extension.
Fill the vase with lukewarm water and add floral preservative. Remove the flowers from the bucket, make a new angled cut in the stem, and arrange them in the vase.
Place the vase where it will receive bright but indirect sunlight. A cool location, away from hot or cold drafts, is best.
Change the water when it gets cloudy, and top it off when needed.