Here in australia, where we are zone 9, we are in the last month of Winter, so you must be in the last, and hottest? month of Summer. I would not even think of planting siberian iris until they are dormant in late Autumn/early winter. If you find them in pots and can plant them without disturbing their roots, and provide them with plenty of water if your soil is dry, then you MAY be OK. As I don't know much about your climate, i can't really say, but it sounds a bit too early to me.

This is a good time to plant but be sure to water if you don't get rain.
In this part of zone 5 summer is fast fading and night time temperatures are down in the 50's. Fall rains should be here soon - it would save me a lot of watering if they would just arrive.