In a message dated 3/21/2006 8:09:47 A.M. Central Standard Time, firstname.lastname@example.org
<<Can anyone tell me what causes the phenomenon of blooming out! I separated and replanted one of my rebloomers last year. Two of the rhizomes bloomed in the fall! Last thing I expected after separating them and I wondered if that had happened to them. I have not ever experienced that to my knowledge. If those 2 rhizomes bloomed out in the fall, will they die this spring? >>
Blooming in the fall is not an indication of "bloom out!" (If that is the question) Fall bloom after transplanting is not uncommon and should not be seen as a problem.
"Bloom out" is when a rhizome blooms on all available fans (season doesn't matter) and does NOT produce increase. Some rhizomes are just teasing and will put up increase during the next season or after a good soaking rain. Others simply will not produce more rhizomes no matter what you do. (I've no idea what causes it, specifically).
You can probably find a lot on the subject in the iris-talk archives. It's always the favorites that "bloom out!" For me it was Orange Star & a killer seedling in the early years, and then Knoble Dragon in 2004/2005!! There have been others but these are the ones that HURT!