Growing the Siberian Iris

When you hear the word “iris,” do you see a big bearded beauty rising up above swordlike leaves? You’re thinking of the bearded iris (Iris germanica), a popular spring/summer garden star. The Siberian iris (I. sibirica), another flower entirely, is well worth your attention, too.

The Siberian iris generally grows 2 to 4 feet tall; withstands wind, rain, and cold; and makes a lovely cut flower.

When Does Siberian Iris Bloom

Impressively, one mature plant can send out more than 20 stems of flowers at once, in a bloom season that lasts from late April to early summer. The Siberian iris quickly fills in spaces in a sunny border and works well at corners, too. Good companion plants are aquilegia, daisies, lupines, peonies, phlox, and pinks.

Best Conditions for Iris

The Siberian iris grows well in USDA Zones 2 to 9. In northern regions, grow it in full sun. It performs reasonably well in light shade where seasons are warm. In extremely hot southern climates, grow it in a shady location. Although it will tolerate dry periods, for best performance, plant it with perennials that you water well all summer long.

When to Plant Siberian Iris

Siberian irises are usually planted in the spring. Space plants about 18 to 24 inches apart. Plant rhizomes with the crowns 1 inch below the soil level and cover them with soil—2 inches deep, if the soil is sandy. To avoid air pockets beneath the crown, make a small hill of soil in the center of the planting hole, place the rhizome on the hill with the roots spread around it, fill the hole with soil, and pack it tight. I like to plant in groups of 3 or 5 or more for a beautiful display.

Keep evenly moist for 6 to 8 weeks after planting. Water once a week during hot, dry weather. Water when needed for at least one full growing season. Just note Siberian irises may not bloom the first year after planting but that they will eventually form large, well-established clumps.

When Do Siberian Iris Bloom

To have Siberian irises in bloom for the longest period of time, include both early and late varieties in your garden. Here are a few examples:

Early Bloomers: 

• ‘Bouquet’
• ‘Indy’
• ‘Pleasures of May’

Late Bloomers:

• ‘King of Kings’
• ‘Liberty Hills’

When to Cut Back Siberian Iris

Remove spent flowers after they bloom to keep seed heads from forming. In late fall, cut foliage to the ground and mulch well after the ground has frozen.

If you wish, lightly fertilize in early spring with an all-purpose garden fertilizer, such as 10-10-10. They can also be fertilized immediately after bloom. Add mulch to conserve moisture.

When to Divide Siberian Irises

After a few years, if large clumps form, some gardeners divide them to ensure continued bloom. Dig mature iris plants in the spring or early summer after they bloom or in the early fall, well before frost threatens. Loosen the soil carefully and pry the rhizomes loose with a rocking motion. Cut the rhizomes with a sharp knife, leaving each new piece with two fan divisions. Plant the divisions, cover with soil to a depth of 1 to 2 inches (as directed), and keep the new plants evenly moist for 6 to 8 weeks after planting.

The Top 12 Siberian Iris Varieties

• Siberian irises come in a wide range of colors—purple, blue, pink, lavender, yellow, white, and bi- and tritones. In a poll, the Society for Siberian Irises (SSI) members put these varieties at the top of their list: ‘Roaring Jelly’
• ‘Over in Gloryland’
• ‘Jewelled Crown’
• ‘Strawberry Fair’
• ‘Coronation Anthem’
• ‘Shaker’s Prayer’
• ‘Lady Vanessa’
• ‘Sultan’s Ruby’
• ‘Lake Keuka’
• ‘Mesa Pearl’
• ‘Pink Haze’
• ‘Somebody Loves Me’

Iris: What’s in a Name?

In Greek mythology, Iris is the name of the goddess of the rainbow. The iris bloom has been the symbol of monarchs and royal families throughout history. One of the earliest paintings of an iris is a fresco in King Minos’s palace on the Greek island of Crete. The palace dates from 2100 b.c.

The Bourbon kings of France, including Louis XIV, adapted the iris bloom on royal banners as the “fleur-de-lis.”

The iris is the state flower of Tennessee, and the fleur-de-lis is the emblem of the city of New Orleans, Louisiana.

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