Caring for established Siberian Iris
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 day lilies 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!
SEASONAL CARE: Throughout bloom season, most Siberians will remain attractive without regular deadheading. Afterwards, however, it is a good idea to remove spent bloom stalks, 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. CHECK TOM'S MEMO ON INSECTICIDE... 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.
~Culture information from The Society for the Siberian Iris