I have been growing purple German Irises for more than a decade. Nineteen months ago I divided them (I did it once before, about 6 years previously) in September, which is the right time to divide irises in our area (central Texas). I gave bags of the extra rhizomes to friends. None of the irises (mine or my friends) bloomed the following spring, which surprised me, since they had bloomed six months after division before. This year, my friends' irises bloomed in March, but mine didn't bloom and show no signs of blooming. Over the last decade, they always bloomed from late March to early April at the latest. They are on a sunny hill (as before), they are healthy, they have excellent drainage, they were planted properly, they got the appropriate amount of natural fertilizer in December and yet, no blooms. We did have a cold snap in mid February, which isn't unusual. I don't understand why they didn't bloom. I wonder what I did wrong. Can anyone give me some tips to help them bloom next year? I'm enclosing a photo of what it looks like when it's blooming.

It sounds like you are doing everything right, but I had to pause when I read "natural fertilizer" because it is usually quite high in nitrogen. Irises may put out a lot of nice foliage in response to high nitrogen, but high nitrogen can increase susceptibility to rot, and it can fail to initiate bloom buds. Schreiner's nursery sells an iris fertilizer, but if you look at the analysis numbers, you'll see it is low nitrogen fertilizer. If I recall correctly, it is something like 6-10-10 or 5-10-10. That first number is nitrogen.

Low nitrogen fertilizer is hard to find online or locally here, but I have indeed found some by searching online and at Amazon. Schreiners' fertilizer is a bit expensive for me.

I sprinkled some Medina's Growin Green 3-2-3 over the iris bed in December. It occurs to me now that I should ask my husband if he fertilized that area, also. He does throw it around in late winter, so it could be he inadvertantly did the iris bed, too. Thank you for bringing that up and helping me figure out what could've gone wrong.