Roses stay fresh longer with sugar
If you get or give away roses that did not come with fresh rose from the nursery, you do not have to buy that expensive.
The same effect you achieve if you! Something! Add sugar or a sip of stale Fanta to the flower water. Then the roses keep fresh longer.
The tip I got from a florist who did not want to buy the expensive rose fresh anymore.
Before that, cut the roses fresh at an angle, so that they can absorb the sweet water even better.
But beware! My grandma used salt from time to time. THAT'S NOT SAFE!