The only successfully container blooming TB's I've seen were in 1/2 barrels.

Put them into a well-drained bed that is allowed to dry between soakings during summer and you'll see bloom again.

I agree with iris gal, you can only expect bloom on bearded Iris in very large containers. But what kind of Iris are they? I. missouriensis, Siberian, Crested, Dwarf Bearded, and some Intermediate Bearded Iris are very unlikely to bloom in your climate. Tall Bearded, Miniature Tall Bearded, Border Bearded, some other Intermediate Bearded, and Spuria Irises are much better choices for your area.

Happy hunting!
Kevin : )

I have had MDB, SDB, IB, BB, MTB, and TB irises grow to bloom in gallon containers, but they certainly would have been better off in the ground.

I'm not recommending container growth. However, it is possible, though far from ideal.

I agree you can have TB bloom in a gallon pot one year if they've had previous good culture. Unusual to get bloom 2nd year ~ not impossible.

A grower I know used 3 gal. pots and the year she didn't get the unsold ones back in the ground there was no bloom on most (TB's).

They've been potted for 6 years. Gradually losing vigor. Even going into the ground they may take 2-3 years to begin bloom.