While I have grown bearded iris for years, I have not experimented much with the advice that I have read. That said, the advice I read long ago was that bearded iris will not bloom if they are planted too deep. The rhizomes should (I am told) be at least a little exposed above the soil level.
It may be chance, but that is how I have always planted/replanted them, and the only failure to bloom I've seen is in the plants this year, which were transplanted much later than they should have been last year. (One of four is blooming.)
I've rarely done much to feed iris, other than keeping a mulch for the worms to work in. They seem to do pretty well in pretty poor clay, though I couldn't say how.
All of that is living in seasonal climates (Ohio and N. Virginia). I never grew iris in a freeze-free climate (though I know they do well).