Dahlias

conditioning of dahlias is crucial.    Cut the flowers early in the morning.  Have a container of very hot water containing dissolved floral preservative and a deep bucket of cool water nearby.   Loosely wrap the flower heads in newspaper so they won't get steamed, and dip the bottom three inches of the cut stems in the hot water for 20 seconds, then plunge them into the cool water.  Remove the paper and leave them in the cool water until you are ready to arrange them.   Without this treatment, the bloom won't last as long.  

courtesy of gardenmaking.com