White Flowering Japanese Roof Iris. This white flowering form of the Japanese Roof Iris has all of the other characteristics of this wonderful selection. This Iris species is superb for the garden with limited space which will only get to 8-18" in height. It prefers some shade in the Deep South and likes uniform moisture. If allowed to get extremely dry, the tips of the leaves will burn. When used in mass, the foliage makes an impressive statement even without its flowers.