When you’re gathering roses from your own garden, take along a container of water and plunge the stems into the water immediately after cutting from the rose bush. It also helps to choose rose buds that are almost ready to open, or have just begun to open, and to gather your rose buds in the early morning.
Once inside, recut the stems under running water and place them in a vase of fresh water. If exposed to air, the cut ends can seal up, preventing water from entering the stems, and shortening the life of your flowers.
Another trick is to use one of the following homemade preservatives and use in place of plain water: Mix 1 teaspoon bleach and 1 tablespoon sugar into 1 gallon of water, or mix 1 cup 7-Up or Sprite into 1/2 gallon of water. The acid will slow bacterial growth and the sugar will provide nutrients to your cut flowers. Roses will also last longer if you can refrigerate them at night and bring them back out during the day.