Fill your vase with water a little lower than body temperature (98.6 degrees Fahrenheit).
Place your roses into the vase to see how much of the stem falls below the water line.
Take your 12 roses out of the vase and use your floral shears to cut off the branches, leaves and thorns that fall below the water line.
Cut off an inch of the roses' stems so they can absorb water more easily.
Create a grid over the mouth of your vase with eight strips of floral tape. Alternately, you can secure your roses together with a rubber band a couple of inches below the blooms. Attach the rubber band securely, but not too tight.
Carefully place the 12 roses into your grid, working from the center outward. If you used a rubber band instead, simply place your bouquet into the vase.