Are Iris Bulbs Heat Hardy?

Bearded Iris

• Bearded irises (I. germanica) grow from rhizomes that spread along the soil surface. Suited to U.S. Department of Agriculture plant hardiness zones 3 through 10, they thrive in most areas of the country except Hawaii.

Siberian Iris

• Siberian Irises (I. sibirica) are slightly less heat tolerant than their bearded cousins, growing well in U.S. Department of Agriculture zones 3 to 9. These trouble-free irises like moist soil in sun or partial shade.

Japanese Iris

• With their large, flat flowers, Japanese irises are show-stoppers wherever they're planted. Growing best in moist soils in U.S. Department of Agriculture zones 5 through 9, they're suited to most of the southern tier of states.

Dwarf Crested Iris

• A woodland native wildflower, the dwarf crested iris (I. cirstata) is a small, spring-blooming iris. It grows well only in U.S. Department of Agriculture zones 4 through 8 and is unsuitable for the warmest areas of the country.

Dutch Iris

• Often sold alongside tulips and daffodils in the fall, Dutch irises (I. hollandica) are real heat lovers. They grow well only in U.S. Department of Agriculture zones 8 through 10.