Siberian irises are among the easiest of all types of iris to raise and bloom in the temperate climatic zones. Their graceful stems, blooms, foliage, and neat habit of growth make them the most adaptable irises for the perennial border and for landscaping. Their handsome foliage is attractive all year, even when the first frost turns them a rusty red-brown.
SOIL: Siberians perform well in most garden soils, but do best if you provide a rich soil containing liberal amounts of organic material, with a mildly acidic pH of 6.0 - 7.0. If your soil tends to be over 7.5 pH, working in sulfur, or acidic organic material such as pine needles or Canadian peat will help increase acidity. In areas where the groundwater is alkaline, repeated acidification will be necessary.
FERTILIZER: Requirements vary depending on your garden soil, but most successful growers use a balanced fertilizer, such as 10-10-10, or a 14-14-14. Fertilize in early spring, and again after bloom season, to encourage growth for next year. Many use foliar feedings monthly with a soluble fertilizer such as Miracid. See also TSI, Spring, 2019.
SUN & MOISTURE: In northern states, Siberians do best in full sun, or at minimum six hours of sunshine. In hot southern areas, protection from the mid-day sun is often a requirement. They enjoy lots of moisture in spring, and will do best if given a minimum of one inch per week during the balance of the growing season, so plant them with other perennials, such as daylilies which also need constant moisture to keep doing their best. They tolerate, but do not appreciate, summer drought.
MULCH: A mulch of organic material will benefit the plants in summer by conserving soil moisture and keeping the soil cooler, and it helps to prevent frost heaving, especially on new transplants. The mulch is also beneficial in reducing weed germination, thereby giving you more time to watch the plants grow and bloom! It can however provide a home for voles and mice that eat the rhizome.
SEASONAL CARE: Throughout bloom season, most Siberians will remain attractive without regular deadheading. Afterwards, however, it is a good idea to remove spent bloomstalks, both for garden appearance and to prevent reseeding. Cut back Siberian foliage only after it turns brown and withers in late fall. Then, cutting off all leaves an inch or two above ground level is recommended.
PESTS: Siberians are more resistant to disease than other garden irises, but do suffer from scorch in those areas where this attacks other iris varieties. They are not immune to the iris borer in those areas where this pest gains the disgust of iris growers. One application of Cygon 2E, or Orthene, applied when the weather hits 70 degrees in the spring will control this pest in most situations, along with good garden hygiene in your spring cleanup. If you have trees or bushes near your garden, remember that borer moths sometimes lay their eggs in trees above the plants, so sometimes a second spraying is necessary after the grubs drop down from their hatching spot.
TRANSPLANTING & DIVIDING: Two to four fan divisions are recommended for transplanting, and the roots must be kept moist while the plants are out of the ground. Plant the rhizomes one inch deep (slightly deeper in sandy soils). Siberian clumps can grow undisturbed for several years, dividing being necessary when either the clumps become crowded or when vigor declines and blooms get smaller. COLD CLIMATES: Spring is the best time to plant or divide, with August as second choice. This gives the plant a chance to establish a good root system before winter rolls in. WARM CLIMATES: Avoid the hot weather periods; many prefer the cooler fall period. If unable to obtain plants at the best time for your area, you may pot them up and put in a protected area. If wintering over in cold areas in pots, be sure to set the pots in the ground, with the tops at soil level. Use of gallon size pots is best for this procedure. In any situation, keep newly transplanted plants well watered at all times, with one inch per week a minimum, and mulch for their first winter.
WHERE TO PURCHASE SIBERIANS? In the back of every issue of the American Iris Society Bulletin and The Siberian Iris is a commercial directory which contains the most up-to-date information listing reputable commercial gardens. Internet users can shop many of these gardens by visiting the American Iris Society website and our list here.