They say that fall is the best time to divide Iris in Texas, but we're not that far away from fall, the first day of winter being Dec. 21. In warm climates such as San Antonio if divided now they will have the opportunity to grow roots and new foliage though the winter and early spring so I think it would be fine to divide them now, or rather tomorrow since it is wet and rainy right now. Sunday and Monday are supposed to be warmer, sunny and clear ... :-)

I never have had a problem with dividing or moving irises at any time, except that they are more likely to bloom the next season if you divide them in August.

In either case, you'll get flowers in 2017, & the irises will be happier & will bloom more heavily than they would in their current crowded situation.

I never have had a problem with dividing or moving irises at any time...

That's been our experience. Only found four ways to kill them: 1. replanting in a low/damp spot where they rot, 2. not moving them soon enough after falling into year-round total shade from surrounding growth, 3. not watering enough after transplanting during late summer drought, and 4. forgetting to replant/give away divided rhizomes..... hate finding those forgotten boxes or pots.

Assumed question was about the rhizome types, but same for Dutch bulbs.
Just harder to locate them for dividing once foliage dies back in the
late spring .

American Iris Society mentions getting them moved a month+ before the first hard freeze, so may be different with the harder freezing further north.

I suppose I will wait until after they bloom or divide some of them and wait until next year for a show. Great info. Thanks!