[swimming with sharks]

My mom's irises didn't bloom again this year so your question spurred me on to research. This is what I've found:

this is based on the irises being the bearded kind:

There are usually three reasons why bearded irises don't bloom:

1) They have become overcrowded. Irises need to be divided every three to four years.

2) They also won't bloom if they're planted too deep, or

3) they receive too much nitrogen from a fertilizer combination high in nitrogen.

It is recommended to dig them up and replant them this summer (For best results, Iris should be planted in July, August or September. It's imperative that the roots of newly planted Iris be well-established before the growing season ends. In areas with hot summers and mild winters, September or October planting may be preferred.) Plant them so that a thumb-size portion of the rhizome is exposed to the sun. Instead of using potting soil I'd add regular bags of garden soil. Fertilize with a fertilizer no greater than 10-10-10.

I'm going to try it with some of mine to see if it works.