Siberian Iris Planting Zone

USDA Map

• The U.S. Department of Agriculture plant hardiness zone map consists of 11 growing zones spread out over the United States. The growing zones indicate winter temperatures. Perennials, like Siberian irises, go dormant in winter. In areas colder than the indicated planting zone, perennial roots die. Each zone between 1 and 11 has a 10-degree Fahrenheit difference in winter temperature. The map indicates the region marked with a number that corresponds to a list of temperature ranges.

USDA Zones

• Siberian irises grow in U.S. Department of Agriculture plant hardiness zones 3 through 9, making them a particularly cold hardy plant. In zone 3, winter temperatures drop as low as -40 degrees Fahrenheit. The soil and snow pack provide some insulation. Bulbs, left out in the open air, freeze at these low temperatures. Siberian irises require winter cool soil temperatures to grow well. In zone 9, winter temperatures drop to 20 degrees Fahrenheit.

Sunset Zones

• Sunset planting zones determine plant hardiness based on climate, rainfall, elevation and latitude and include micro-climates in each area. Siberian irises grow in Sunset zones 1 through 10, 14 to 23 and 32 to 45. The climate zones are divided up into 23 regions throughout the United States. The Sunset zone map provides detailed indications for the different zones including Western and Eastern Washington, Western Oregon, Northern and Southern California, Alaska, mid-Atlantic and Great Lakes, to name a few.

Planting and Growing Siberian Iris

• Plant Siberian irises in the fall before the first hard frosts. Dig a planting hole slightly deeper than the root system. Spread out the roots in the hole and cover with 1/4 to 1/2 an inch of soil. Spread a 4- to 6-inch layer of mulch over the area to keep moisture in the soil and provide insulation. Pull back the mulch in spring to make room for new shoots. Plant Siberian irises in full sun or part shade and damp, consistently moist soil. Divide every three to five years.