Iris Iris Size: 4 to 40" high by 10 to 24" wide. Hardiness: Zones 3 to 10. Heat Zones: 9 to 1. Habit: All irises bear complex flowers made up of three standards (petals), usually upright in the center of the flower, and ringed by three falls (petal-like structures called sepals), extending outward. Culture: Full Sun to light shade.