Swans in Flight Siberian Iris thrives in full sun to partial shade and requires well-drained, slightly acidic soil. Ensure the soil remains consistently moist, especially during the growing season. Divide clumps every three to four years in early spring to maintain vigor and encourage blooming. Deadhead spent flowers to promote a tidy appearance and focus energy on root development. Fertilize lightly in early spring with a balanced fertilizer to support healthy growth.