travis to the iris forum.
my experience in this location (10a) has been, irises in large pots do increase better. i grow mine in 15- 20 gal. size pots because i really don't have much in-ground space to grow. i have very sandy soil with nutrient poor soil. i also grow them in smaller containers, but have to repot every year for the 3+ gallon containers. that said there are a few problems for me:
1. because of my long season growing area, my irises increase quite substantially. which in turn, requires more frequent repots (seems that most others on the forum maybe able to leave their irises in 15-20 gal. containers for up to 3 yr. i've found that after 1 1/2 years mine are too packed. this makes extracting the iris for repotting even more difficult.)
2. it's quite expensive to buy 20-30 bags @ $15/bag even at warehouse stores.
3. difficult for me to wrestle the iris from the larger pots my age and stature
on the positive side:
1. easier to control its nutrition and water needs
2. results in better than average bloom rate
3. higher elevation, easier to see blooms
all things weighed and being equal i will always have a few in pots as long as i have help at repotting. i have really cut down on the quantity of pots, and have promised self to do more because the work involved is slipping beyond my ability to keep up.
hope this helps, travis, and good luck in your venture. it's a very rewarding one, or there wouldn't be so many passionate, enthusiastic members on this forum with iris virus.