Ok Lizz,
First off what do the irises in the bags look like?? Nice green fans or dried up? Are the Rhizomes nice and firm or are they dried up?
Usually the best time to plant irises, is in the fall, but as long as the plants are healthy you can plant them anytime. They need full sun and only water until you see new growth. Usually with irises you divide about every three years. They also need to be planted 12 -24 inches apart, the closer you plant them the sooner they will need to be divided
Do not plant them too deep in the ground, the rhizome should be at ground level. Planting too deep results in no blooms.
and last but not least..don't be surprised if the beauties in the bag are not what they are marked to be..Big box stores are famous for selling irises that have just been tossed into a pile and then stuck in a bag. So dont plan a garden based on what color these irises are suppose to be!

littlebit