If you want a grass that practically grows itself, this is your plant — but the secret is restraint. Mexican Feather Grass wants lean, gritty, fast-draining soil and a baking spot in full sun, so resist the urge to amend with rich compost or feed it. Rich soil and overwatering are the two most common ways gardeners kill it; it flops, rots at the crown, and sulks. Sow seed in spring once the soil has warmed, pressing it onto the surface since it needs light to germinate, or set out plugs about a foot apart and give them a single establishing season of moderate water. After that, leave it alone. In late winter you can comb out the old foliage with your fingers (gloves help) rather than shearing it hard — it resents a buzz cut. A real word of caution: in mild Mediterranean climates it self-sows aggressively and is considered invasive in parts of California and Australia, so deadhead before the seed ripens if you garden where it might escape.
Rust
Orange to brown raised pustules on the undersides of leaves, with yellow spotting on the upper surface. Heavy infections cause leaves to yellow and drop.
Remove and destroy infected leaves. Avoid overhead watering and improve air circulation. Apply a sulfur or copper-based fungicide if it spreads. Clear plant debris in fall.
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.