Douglas iris is a native evergreen perennial of California's coastal grasslands and scrublands, ranging from southern Oregon to central California. It forms spreading clumps of narrow, arching leaves and bears lavender to violet flowers in late winter through spring. Tolerance of coastal fog, light drought, and clay soils makes it well-suited for Pacific Coast native plantings and erosion-prone slopes.
Plants spread by rhizomes and self-seed into loose colonies over time. They perform best with sharp drainage and full sun near the coast; inland, afternoon shade and reduced irrigation help prevent stress. Dividing crowded clumps every four to five years maintains vigor. Summer irrigation should taper once flowering ends, as wet, warm conditions around rhizomes encourage rot. Slightly acidic, low-fertility soil discourages rank growth and promotes natural habit.
Native Californians harvested the tough leaf fibers to make cordage, fishing nets, and basketry twine — leaves were dried and twisted into strong, durable strands. Indigenous groups also recorded medicinal applications for the plant, though the fiber use is its most thoroughly documented practical history.
Fungal leaf spot
Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.
Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.
Crown Rot
Lower leaves yellow and wilt; the base of the rosette turns brown and soft, sometimes with white fungal threads at the soil line. Plants collapse in wet conditions.
Remove and destroy affected plants. Improve drainage and avoid overhead watering. Do not mulch directly against the crown. Space plants for airflow and avoid replanting in the same wet spot.
Bacterial Soft Rot
Rhizomes turn mushy and foul-smelling; foliage yellows and pulls away easily at the base. Often follows borer damage or overly wet soil.
Cut away all soft tissue back to firm rhizome, let it dry, and dust the cut with sulfur. Improve drainage and avoid burying rhizomes. Destroy badly infected plants.