» Unlike most spring bulbs, bearded iris don't require a period of cold to produce blossoms, making them perfect for areas with mild winters. They are also extremely drought tolerant, good for areas with little or no summer rains. Bearded irises are not actually bulbs, but rhizomes, a kind of thick brown root. Hardy in zones 3-10, the rhizomes need plenty of sun to bloom well and regularly. They do best in well drained soil, but will tolerate less drainage in drier areas.