Cortaderia selloana is a large clump-forming grass native to the Pampas grasslands of Argentina, Brazil, and Chile. Gardeners grow it for its dramatic scale — clumps can exceed 10 ft — and the tall silvery-white plumes that emerge in late summer and persist into winter. Dried plumes are a durable material for floral and decorative use.
It performs best in full sun and well-drained soil, tolerating drought, coastal salt spray, and low-fertility soils once established. Female plants produce the most pronounced plumes. The leaf margins are sharply serrated; wear heavy leather gloves when cutting back or dividing. Cut old foliage to 12–18 in from the ground in late winter before new growth begins. Dry accumulated leaf litter in the crown is a fire hazard in dry climates. Pampas grass is classified as invasive in California and several other warm or coastal regions — a single female plant can set up to 100,000 seeds — and local ordinances may restrict its sale or planting. Remove seedlings that appear outside the intended area immediately.
Root rot
Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.
Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.
Helminthosporium Leaf Spot
Small oval to elongated tan or brown lesions with reddish-purple borders appear on leaf blades and sheaths. In severe cases, blades yellow and die back from the tip downward.
Remove and dispose of heavily infected foliage. Avoid overhead irrigation and improve air circulation by thinning dense plantings. Fungicide applications are rarely warranted on established native grasses; correcting site conditions — spacing, drainage, and fertility — is the primary control.
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.