Rinse your vase with hot water and a mixture of 1 tablespoon dish-washing detergent in 1 cup water. Scrub the inside surface of the vase with a bottle brush and rinse it again. Soak the vase in a 5-percent bleach solution for five minutes and rinse. A thorough cleaning removes bacteria that can attack roses.
Water your rose plant the night before you plan to cut the blooms. The extra water will give the flowers better staying power. As you water your plants, take note of the flowers you want in your bouquet. Choose the blooms that are just starting to unfurl because you will get to enjoy the open flowers for longer.
Cut your flower stems at an angle to increase the surface area through which they absorb water. Do this early in the morning after the dew has just dried. Hot days make roses deteriorate faster.
Fill the vase or a bucket with lukewarm water, and immerse the stems in the water and cut the rose stems again to remove air bubbles. Cut them so that every stem is about 8 to 10 inches long. Remove the leaves that will fall below the water line, because they can promote bacterial growth. Remove the thorns to prevent injury.
Place the roses and the lukewarm water in a cool, dark room for one hour, placing the flowers so that most of the stems stay underwater but the blooms remain dry. Refrigerate the roses for two hours. These steps help the flowers last longer.
Gather the flowers in your hand and arrange them so that the tallest one is in the center, forming a dome shape. Wrap the stems together with wire to maintain the shape.
Pour water into the vase and add a floral preservative, which comes in powder and liquid forms. Place the bouquet in the vase, keeping the leaves above the water surface.