Adding sugar to the vase water of cut flowers helps blossoms last longer. When flowers are cut before they are fully developed, a sugar-and-water solution is also helpful in stimulating flower buds to open.
The amount of sugar needed varies depending on the flower. The majority of flowers benefit from maintaining a solution in the vase that is made of 2 percent sugar. Gladioli last longer with a higher concentration of sugar, ranging from 4 to 6 percent. Zinnias can be damaged with a solution of sugar and water any higher than 1 percent. A 1-percent sugar solution consists of approximately 2 teaspoons of sugar in 1 quart of water. It is important to test the solution on a few flowers before immersing the entire batch.
While a sugar solution extends the life of cut flowers, it also creates an ideal breeding ground for microorganisms. In order to prevent the growth of unwanted bacteria, biocides should also be added to the water. Bleach is a common household biocide. Adding 2 teaspoons of bleach to 1 quart of water helps prevent bacterial growth. A slight discoloration on the stems of some flowers can occur with the addition of bleach, so it is important to test the solution before treating the whole bouquet. A fresh solution of sugar, water and biocide should be made daily.