The key to caring for cut flowers is to remember that, even when cut, they are still living. Cut flowers drink, breathe, and eat, just as they do when they are connected to their plant. Some flowers, such as tulips, even continue to grow after being placed in a vase.
Most of the little packets of commercial floral preservative that come with cut flowers contain the basic components needed to support the life of cut flowers in their vase environment: a chemical biocide, an acidifier, and sugar.
