Hi Charlotte.

I know what you mean. Some flowers just don't last very long do they, or not long enough. There are a few things you can do but remember that this will only increase their life a little longer.

If you ever get a bunch of flowers, re-cut the stems back an inch under water and put into the vase one at a time immediately. This stops any air bubbles getting into the tubes that carry water up the stems.

Drop an aspirin in the water of the vase to help them last longer too.

The last thing, try and place your flowers away from a heat source, ideally if possible, in the coolest part of the house.

I haven't heard of the aspirin one Fractal :)
I put in a drop of bleach (a tiny drop ) and half a tea spoon of sugar.The bleach keeps the water from smelling and the sugar acts as a feed.
I also re-cut the flowers after five days and change the water again.