Once the iris rhizome blooms, it will not bloom again. That's true even on re-bloomers. I don't like to cut out the spent rhizome until it softens and dies, as it gives nourishment to the young beginning rhizomes. After it's soft and dead, then I will remove it. You might be thinking about the article that Kent wrote about thinning as apposed to dividing. I'm not sure where that is, but maybe you could search for it.
