Hold the stems of the bouquet in a bucket of warm water and cut the bottom of the stems at a 45-degree angle.
Place the bouquet into a glass vase filled halfway with warm water. Pull off any submerged leaves from the bouquet.
Pour in a can of lemon-lime soda until the vase is filled near the top with half water and half soda. The sugar in the soda helps the roses stay fresher.
Mix in a packet of flower preservative.
Place the vase near a window where the bouquet receives sunlight. Too much heat or sunlight causes wilting, but indirect sunlight is beneficial.
Replace the soda and water solution in the vase daily, and rinse the stems under a faucet when you do.
Lower the temperature in the room in which the bouquet is kept. The hotter the temperature, the faster the bouquet decays.