I think moving irises when they go dormant in the heat is better for the plant. The heat is hard on the plant mover. Usually vendors dig and ship in July Aug and some in Sept. most of the vendors that I do business with like to ship from late July thru mid or late aug. this is usually after the spring bloom and full growth of leaves.
After the hotter months, and the irises break dormancy, you will see a period of growth before winter.
