Beardless Siberian iris bloom in May and June with intricate blooms Each plant has numerous stems and the plant will form large clumps. Each stem will have 3-4 blooms. The erect sword-like leaves are attractive even when not in bloom and unlike other iris, will not die back after the plant flowers - which makes them ideal for landscaping. Plants prefer full sun or light shade and rich, moist, well-drained soil, although they are not fussy.