Really -- good clean water is the best thing you can use.

But here are some things you can do to maximize vase life:

1. Pick the blooms on the tight side. Some will open fine if the sepals are all the way down. A smart rose exhibitor said, "Pick 'em tight, and they'll be all right." He was correct. If they're fully open, don't bother.

2. When you pick your blooms, RE-CUT the stem under water.
The cut stem is blocked by air, and will not efficiently take up water, in a vase. If you stick the stem end under water, stick your clippers in the water, and re-cut the stem under water at a steep angle, you'll eliminate that problem. Making your cut at a 45 deg angle or better offers more surface to take up water.

3. Run a basin -- such as a dishpan -- full of warm (not hot, but warm) water. Lay the blooms in it, with the bloom head propped up on the side, and the stem and foliage in the water. Set them in a dark room, and allow them to "repose" for an hour or two.
They will take up quite a bit of water, and will subsequently last longer in a vase.

4. REMOVING the foliage that will be under water eliminates a source of dirt and bacteria, and is helpful for that reason.

5. Use a CLEAN vase. Bacteria is your enemy. When you empty a vase, wash it with soap and water. If it still looks dirty to me, I will let it sit with white vinegar in it, then rinse it well. If I am REALLY in a hurry, I will swish some rubbing alcohol around in the vase. Again, rinse it well.
Fill with clean, pure water.
Watch the water level in the vase, and make sure it remains full enough for water to be available to the stem end.
You can even pour the old water out, and refill with fresh.
Of course, some roses have an excellent vase life, and others don't.

6. It has been suggested that a few drops of GIN will "feed" the bloom (and I'm sure the alcohol kills bacteria). Do I do this? No. I LOATHE Gin, and have none in the house. I use plain old water, which really works well.

Jeri

Thank you for explaining the directions....it makes a difference with compliance and results.
Susan

All that jeri said, and then there's the magic of refrigeration . Wish I had a florists frig to pop them into every night. The following pics are of Just Joey, Color Magic and floibunda Eureka, having been cut very full, and refrigerated, in and out, for a week.

JJ has wilted a bit after a week.

Thanks for this information. The bacteria removal and reposing steps are new to me. Very helpful. Mary

I've just finished trying 7-Up pop mixed with water. It worked waaay better than water and floral preservatives. Blooms were fine for a week and a half with me doing no further stem cuttings than the first one (florist roses).
Carol

Carol beat me to it, regular 7-Up or Sprite replacing gin in Jeri's step 6, I would say 4 tablespoons per quart of water. You can also use chlorine bleach, ~1 teaspoon per quart of water, mixed with 1/2 teaspoon of sugar.

Thanks for your responces