![]() In other words, the best time to plant irises is in fall. Nursery grown iris plants can be installed at any point during the growing season, but for optimal growth, all irises should be planted or transplanted after the risk of extreme heat has passed and before the ground freezes. When to Plant Irises The iris plant is best planted in the fall. These irises typically possess the cold tolerance of a parent iris from one of the other groups. Take exception with aril hybrids, or arilbreds as they are known. The cultivars of this iris thrive in mountainous or desert regions with arid conditions and can grow in sandy soil. Aril Iris: 7-10 This species grows well in desert and mountainous areas.Īril iris species (oncocyclus and regalia) are native to the hot, dry climates of Central Asia and the Middle East. Hexagonae) will not survive harsh winters, but are highly tolerant of humid summers, hot sunshine, and high temperatures. Native to the southern regions of the United States, Louisiana irises (ser. Louisiana Irises: Zone 6-10 Louisiana Irises grow well in hot and high temperatures. Iris Germanica is one of the most popular species amongst those mentioned here and are usually what many gardeners think of when looking at irises in seed catalogs. Irises in these species (germanica, siberica, and ensata) will not be damaged by severe winter temperatures during their dormant periods, but they are somewhat vulnerable to extreme summer heat. German, Siberian and Japanese Irises: Zone 3-9 Japanese iris tolerate harsh winter temperatures well. Members of these groups will not perennialize reliably in parts of the world below zone 5 or above zone 9. Irises in the dwarf (reticulata) and German (x hollandica) species are grown from bulbs rather than rhizomes. ![]() Knowing the major iris groups’ hardiness category is the first step in determining the best time to plant, so let’s look do a quick break out: Dwarf and Dutch Irises: Zone 5-9 Dutch Irises are grown from bulbs and grow well in zones 5-9. Iris species have such broad differences in their growing profiles that the general hardiness zone recommendations for the genus are 3-10, but that doesn’t mean all irises can grow in all of those zones. So, if a plant is said to be hardy to zone 5, that means it can withstand winter temperatures that fall in that range during its dormant period. If you’re looking at central Iowa, for example, you’ll see that it falls mostly into zone 5, which has average low temperatures of somewhere between -20 and -15 degrees. The map is color coded from the coldest and lowest numbered zones in the northern hemisphere to the warmest and highest numbered zones in the southern hemisphere. The USDA Plant Hardiness Zone Map, which divides North America, Europe, and the rest of the world into 13 regions based on 10 degree differences in average low temperature, is considered the standard reference for agriculture and horticulture planting recommendations. Hardiness Zones Hardiness Zones serve as a limiting climatic factor for plant life.
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