Start with a very clean vase. Fill it about halfway with fresh, cool water. Add the cut-flower food to the vase. Hold each stem next to your vase to gauge how much you'll need to trim. Remove any leaves or flowers that will fall below the waterline; submerged leaves and flowers rot and encourage bacteria that shorten bloom life. Using a sharp knife, cut stems at a 45-degree angle. This prevents them from sitting flat in the vase and allows for better water absorption.
Recondition delphiniums every two to three days: Recut the stems, change the water, and add nourishment. Use the extra pack of cut-flower food with your first change of water. To nourish the flowers after the flower food is used up, refill your vase with a solution of one teaspoon of sugar and two drops liquid bleach per gallon of fresh, cold water. Display your flowers away from fruit and vegetables, which produce ethylene gas as they ripen; this causes cut flowers to deteriorate rapidly. Keep flowers in a cool area out of direct sunlight.