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Siberian Iris

Siberian irises are among the easiest of all types of iris to raise. They are also the most adaptable irises for the perennial border and for landscaping. Their foliage is attractive all year, even after the first frost when it turns rusty red-brown. Siberian irises are primarily found in Central Europe and Asia.

When to Plant:  Best time to plant Siberians is in September. Plant immediately after receiving the rhizomes.

Where to Plant:  Siberians are adaptable and hardy. They love full sun but will grow in light shade. In areas of extreme sun and heat, it is suggested that Siberians have some afternoon shade protection. Plant where they will receive at least three hours, preferable six hours of full sun daily. Because watering is similar to other garden perennials, plant Siberian iris with daylilies or similar plants.

Soil Preparation:  Siberians prefer a rich acid soil with lots of organic matter, although they will grow almost anywhere. Soil pH needs to be mildly acidic pH (6.5-7.0). If the soil is over 7.5 pH, work in sulfur, or acidic organic material such as pine needles or peat to help increase acidity. In areas where the groundwater is alkaline, repeated acidification will be necessary. An organic mulch will benefit the plants in summer by retaining moisture and cooling of the soil. A mulch in the winter can help prevent heaving and thawing problems.

Basic Planting Steps:  Siberian rhizomes will arrive moist, wrapped in paper toweling, cloaked with plastic, and rubber banded to keep them moist until planting time. Two or four fan divisions are recommended for planting and the roots must be kept moist. Plant the rhizomes one inch deep (slightly deeper in sandy soil). Plant 15" to 18" apart.

Watering:  Siberians like lots of moisture in the spring and can survive dry periods in late summer months, but clumps will be healthier if kept moist all summer. Siberians do best if given a minimum of one inch of water per week during the growing season. They can tolerate drought. Too much water is one of the Siberian’s worst enemies.

Fertilizing:  An application of fertilizer higher in nitrogen in the Spring, and a second application of a balanced fertilizer (10-10-10) or (14-14-14) at the end of the bloom season. Foliar feedings monthly with a soluble fertilizer such as Miracid is suggested.

Bloom Season:  Siberians normally bloom at the end of the tall bearded season, 24-34 inches tall.

General Garden Care:  In the late fall cut the foliage back to the ground. After bloom, remove the bloom stalks or the blossom heads to prevent seeds from forming. Siberian are more resistant to disease than most other garden irises. They may get iris borer that can be treated with Cygon 2E in the spring. Other than the borer, Siberians are almost disease free.

Moving & Thinning:  Some literature suggests digging and dividing right after bloom. Other literature suggests early fall (September) as the best time to thin clumps. Transplants must be kept moist during the thinning process. Literature suggests dividing Siberian iris after 4 or 5 years if increasing the number of clumps is desired. Otherwise, clumps can grow undisturbed for several years, dividing only with overcrowding conditions, when vigor declines, or when blooms get smaller.

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