Also, we use the following for exhibition roses we grow. . .
As previously directed, re-cut the roses but do this cut under warm water. (In a pail or the sink just so the end is submerged). Be sure the fresh cut ends remain submerged. Then prepare your vase. Mix about two cups of warm (not hot) water with two teaspoons of common sugar and one teaspoon of ordinary laundery bleach. Assure the sugar is well dissolved. Place the water in the vase and immediately insert the roses. The rose ends seal themselves when cut and exposed to the air, so you are re-opening them. The sugar helps feed them, somewhat along the lines of Ethel's good advice and the bleach eliminates bacteria and even viruses that can attack a fresh cut rose. Change the water after a couple of days following the same process... Some exhibitors also use a splash of real (not bottled) lemon juice in the water...