Have you stripped off the leaves? I was told to cut the bottom of the stems in lukewarm water very early in the AM, use hair spray on the flowers and use unbuffered aspirin in the water (or ask florists for some of their life extending compounds distributed in packets).

Yes, I do strip off the leaves, and I do cut them in a sink of lukewarm water....but only on the day I bring them in...I will try doing it again. I have never tried hair spray either. Yes, I do put preservative in the water. I will follow your directions and see what happens....thanks

See this link

Here is a link that might be useful: hydrangeas as cuts