If they're tall varieties, they'll need 12 inch pots, or they won't do well. John Innes No. 2 is probably the best compost to use - you need something that's light and drains well, so although pots with John Innes feel heavy when they're wet to move around, the compost itself is free draining.

You might be interested in reading the information in the link below

http://lifeonthebalcony.com/anyone-can-grow-iris-in-a-container/

Thank you for suggestion....John