Many schemes to extend the life of cut flowers are out there. One of the most popular is to add Sprite or a similar clear soft drink to the water.
A technique that’s free: put ice in the water.
Using a sharp nipper or knife, trim rose stems on an angle. Place the trimmed flowers in a jar or vase with cold water and ice.
Each day, nip a little off the stem ends—always at an angle—and refresh the vase with more cold water.