Well here's an interesting observation -- and mostly in response to Betty's post above -- it occurred to me today that I have Irises that I have dug up and left lying out on top of the ground where I intend to plant them, and they're just fine. The leaves are green, the roots are only a little dried out -- and if I planted them tomorrow, I know they'd take root and be fine. But I have Irises that have been planted for a month that don't look as good as the ones lying on top of the ground. The only difference is water. The planted ones have been blessed with my watering endeavors -- the ones on top of the ground only get a grazing of water when the hose passes over them. And these are all in the same area with each other, so all other elements are identical.
Conclusion -- I need to water less. I need to grit my teeth and ignore those rhizomes that are planted and whose leaves are dried up in this intense heat, and have confidence that they'll be fine. Or at least, hope for the best.
Sometimes this is hard.