Growing Siberian Iris

'Caesar's Brother'

Siberian irises are favored by many gardeners  over the more popular bearded irises for their ease of maintenance, longevity, and disease and pest resistance. Their flowers are smaller than bearded iris blooms, but their grass-like foliage looks attractive all season long. Siberians are also more cold and heat tolerant.

Siberian irises are mostly hybrids of two southwest Asian species, I. sibirica and I. sanguinea (USDA hardiness zones 3-9). The narrow, grass-like foliage forms a vase-shaped clump to 2 feet high. Autumn foliage turns rusty brown in late fall. Flowering stems rise above the foliage to 3 feet tall in May-June.

Siberians perform well in most garden soils, but are at their best in humus-rich, mildly acidic soil. In spring feed with 10-10-10 or an equivalent granular fertilizer. In early summer apply a water soluble fertilizer such as Miracle-Gro™ or Jack’s™.

In Northern states (zones 3-6), Siberians want full day sun (or 6-hours minimum). In Southern areas, shelter from the mid-afternoon sun. Ample spring moisture is key, along with adequate rainfall during the summer. These iris clumps tolerate moderate summer dry periods of a week or two.

Mulch iris in spring to conserve soil moisture and prevent weed infestation. Voles and mice may munch on rhizomes. Remove spent bloom stalks, and brown and withered leaves to keep planting looking attractive. In late fall cut back all leaves 1-2 inches above the ground.

Siberian irises are generally pest-free with very little susceptibility to the two main problems of bearded iris, namely iris borer and bacterial soft rot. Plants tolerate deer and rabbits.

Divide big healthy clumps into 2-4 fans in either late summer or fall, depending on where you live. In northern zones spring or late summer are the best time to plant or divide. In southern climes, early fall is a better time. Clumps can grow undisturbed for several years, unless they become crowded, plant vigor declines, or bloom size declines.

Over 200 varieties are available, principally from online iris nurseries.