There is a vast variety of smaller species Iris that are perfectly suited to the rock garden - many of these originate from hot summer/cold winter areas and require sharp drainage.
I'm not yet much into these special irises (maybe someday - hopefully other people can suggest and show some) but here are a few little guys that are well suited to the rock garden:
Iris danfordiae:
Iris taurica (a new planting of a fairly easy species):
Iris sp., Burdur, Turkey:
Iris taochia:
Iris mandshurica:
Iris taurica - yellow form:
Iris timofejewii:
Iris suaveolens - yellow form; Rick grows these much better than I do!
Iris chamaeiris:
