Although it is naturalized in Japan, it is native to China, where it was planted in thatch roofs to help bind them against strong wind. It is one of the most shade tolerant of all irises. Iris tectorum is an example of the great diversity of exotic Iris species coming into the nursery industry. Flowers appear in late spring and come in lavender, blue, or white. You can grow Japanese roof iris in moist well drained soil, for example, around ponds and fountains, and is hardy in USDA Hardiness Zones 4 through 9. You can find it growing in the Japanese Woodland in the Asian Collections.