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.

Growing Spuria Iris Worth The Challenge

photos courtesy of Iris City Gardens

Jimmy Turner, Dallas Arboretum horticultural guru, gave me this idea. Growing spuria iris in the Southern Appalachian region can be quite challenging. Hardy to USDA zone 5, spurias are dormant (asleep) during our usually hot, dry summers. A wet summer is a real “downer” for spurias.
Spuria irises bloom two weeks after the popular tall beard iris. They grow and flower best under full sun. Spurias are not choosy about soil type and pH. Bloom stalks can reach 4+ feet in height in a good garden soil.
Foliage dries up in the heat of summer, very natural for spuria iris. Gardeners should not attempt to revive them with irrigation. Autumn showers revive plants. Once growth re-starts, plants hate to dry out.
Spurias need one year to become established. Space plants at least 3 feet apart. Divide them every 5 years. Natural rainfall in our region is usually plentiful. The easiest way to kill spurias is to mulch and overwater them.
You may purchase spurias from several mail order nurseries or local nurseries which specialize in iris. Personal shopping emporiums include Iris City Gardens in Nashville, TN and Heritage Gardens in Greeneville, TN.