FRESH CUT FLOWER FOOD FROM SUPERMARKETS

My suspicion is they are all exactly the same but I don't know.

What they contain are simple sugars (to persuade the flowers, particularly unopened ones, that they have enough energy to actually develop and open), a ph corrector (lord knows how that works, rather depends on the ph of the water you're using) which largely prevents unwanted bacteria from growing, and some other unnamed substance which keeps the stems from closing themselves off at the bottom, which would prevent uptake of water. I can't find any difference between, say, the chrysanthemum one and the rose one, and I've certainly used one that says roses on other flowers in a vase without any adverse effect.
In some experiments, adding sugar to the water did just as good a job, but I've not tried it.

You can make your own. I wanted to extend some cut roses and googled flower food - it contained bleach, lemon juice sugar and water - it worked well.

Lemonade works as well.

Tastes nicer too!!

Yup that is what the daughter-in-law uses