Answer: Iris can fail to bloom if they're overcrowded, they're not getting enough sunshine, or the rhizomes are planted too deeply. It sounds as though now would be a good time to dig your irises up, divide them and then replant in a sunnier spot. If you do this now, they will bloom for you next year. Start by digging all the plants up. Cut or break off the old portions of each rhizome, leaving only the part that has leaves attached. Replant them in shallow holes or trenches, just barely covering them with soil. Space each plant about 12" apart.
Best wishes with your irises!
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