If floral foam is used, make sure it is always thoroughly saturated. In a clean vase mix the floral preservative with room temperature water, in the proportion recommended on the package. Add lukewarm to cool water as needed, avoiding water from a water softener. Floral preservative provides sugars, balances pH, and limits bacterial growth. The use of flower food has been shown to increase the life of fresh flowers by several days.
Individual packets are available wherever cut flowers are sold.
Check your arrangement daily to make sure it has plenty of clear, fresh water. If the water appears dirty after a couple of days, replace it completely. If some roses should start to droop their heads prematurely, it may be due to air trapped in the stems. This simple setup will help your flowers absorb cut flower food, while eliminating stem-clogging bacteria. Then, let the roses float on the water surface with the stem ends below water and the rose heads in a straightened position.