Hydrangeas have very specific care instructions to keep them living and looking in top condition like they do when you see them in the florist
They need deep water (fill up your vase) and to be kept out of direct sunlight. Top up the water every couple of days and if you’re feeling like putting extra effort in, trim the stems at the same time. If your hydrangeas go all limp and floppy this will be because of lack of hydration (they absolutely love water hence the name ‘hydra’ngea).
You can revive limp/floppy hydrangeas by dunking their heads in water and leaving them submerged for half an hour, then putting them back in the vase with their stem trimmed.
You would expect a week minimum longevity out of a hydrangea in a vase, however sometimes they can last weeks on end!
With any natural product there is an element of unpredictability and although I always use the best growers even then you can get a rouge bunch which doesn’t do what it should.