Plant Blue Flag Iris in early spring or fall in a sunny location with well-drained, acidic to neutral soil. Space rhizomes 12-24 inches apart, ensuring the top is just above the soil surface. Water regularly to keep the soil consistently moist, especially during dry spells. Fertilize with a balanced fertilizer in early spring. Remove spent flowers to encourage more blooms and cut back foliage in late fall. Divide clumps every 3-4 years to prevent overcrowding.