according to yesterdays RHS Chelsea flower show you should wait 8 weeks after flowering before you cut the leaves off to allow the goodness to go back into the bulbs and don't tie them up!
I may be a bit unorthodox but I lifted mine from the planter (all in one piece) and put the whole lot into a plastic bag, leaving it in the open so the rain could still reach them and to day I have been able to bring them indoors properly cleaned and ready for storing. I needed the planters for my new azaleas.