@peggy8b
soil, water, weather conditions and fertilizer all seem to effect the size, growth and vigor of the iris plants, rhizomes and flowers. plus the ph, and composition of the garden soil.
there are many articles from various growers that are informative. off the top of my head, winterberry gardens comes to mind. they are listed in iris forum's alphabetical, flagged list of iris growers at the top of the iris discussion board. hope this helps getting started?