Iris should be planted in July thru September. The roots need to be established before the growing season ends.
Iris like full sun and good drainage .Plant them about two feet a part. This will give you room to grow a nice specimen. When planting, spread the roots out in the hole and add amendment to the soil. The rhizomes should be exposed or covered only 1" or so.
Be careful not to over water this will lead to rot .Fertilize with bone meal or fertilizer low in nitrogen. Nitrogen will promote rot.