I did my irises this time last year. They didn't bloom as well this spring, but they never do after dividing them. I think anytime the ground is workable you can do it.

Fall is always the best time to plant and transplant here in Georgia since our mild winters allow root systems to develop without being subjected to the stresses of summer's extreme heat and drought.

Keep in mind that this fall has been very dry so new plantings will need regular watering.