Paint them! LOL, seriously, though, I use those flower food packets that you can purchase or that come with the flowers if you buy them. I change the water frequently, cutting the bottoms, but I've noticed some flowers won't stay fresh if they weren't fresh to begin with.
It's not always easy to purchase good-quality fresh flowers, so that's why it's best to grow them in a garden and cut them. However, there's a problem with that, depending on where you're located and the weather.
Hydrangeas are always challenging to keep fresh. There are all kinds of tricks and tips about sticking the heads in cold water, and there are a bunch of them online.
I have never heard of any flowers that would last four years. interesting.