The best time to transplant iris is immediately after they bloom. At that time, the rhizome (not bulb) creates new roots. The old roots will wither and die back, but can be used to "anchor" the rhizome until new roots emerge. The rhizome should be settled into loose ground about 1/2 way above ground. They should sit "like ducks on a pond". It will be necessary to prop them with rocks or something to hold them in place since they will be topheavy. Leave the leaves intact, or trim them to @ 6" long.