Canadian sphagnum peat will lower the soil pH and also adds organic matter. Japanese irises do well in partial shade to full sun. They are excellent plants for moist soils near streams and ponds. Japanese irises, hardy in zones 4 to 9, don't have any serious pest problems. Plants can be left undisturbed for many years.
Flowers are pale blue to violet with white or yellow crests on their falls.
Plants bloom in mid-spring. Crested iris performs best in well-drained soils in partial shade. It is hardy in zones 3 to 9. Because of its small size, crested iris can be grown in front of the perennial bed or border. It also can be naturalized in the woodland garden.