Helictotrichon sempervirens aka Blue Oat Grass

Helictotrichon sempervirens, or blue oat grass, is a perennial ornamental grass. It belongs to the grass family, Poaceae. Its native range runs from southeast France to Italy. This cool-season grass forms dense, rounded clumps with a bristly look. It grows at a moderate rate. Garden plants often reach 2–3 feet (0.6–0.9 metres) tall. Their spread is about 1–2.5 feet (0.3–0.76 metres). RHS gives larger limits of 4.9 feet (1.5 metres) tall and 3.3 feet (1 metre) wide.

The narrow leaves give the mound a fine texture. Their blue to silver-grey tones provide the main garden interest. Each blade ends in a sharp point and curls inward. Leaves may reach 1.5–2 feet (0.46–0.61 metres) long. The clump stays green through winter in mild climates. In colder places, some leaves turn brown or tan. The plant looks like blue fescue but grows much larger.

Upright flower stems rise well above the leaf clump. Small blue-brown flowers hang in loose, one-sided panicles with arching tips. Missouri Botanical Garden lists June bloom. NC State places flowering in mid- to late summer. The flower clusters turn gold as autumn arrives. Each small, dry fruit is an oval, tan caryopsis.

Grow blue oat grass in full sun and well-drained soil. Shade can cause the leaves to flop. It prefers dry to moderately moist soil, with neutral or alkaline pH. Sandy and loamy soils suit it well. It also tolerates clay, provided winter wet does not linger. Drier soil brings out the blue leaf colour. The plant withstands drought but struggles with high heat and humidity. Sources place it in USDA zones 4–8 and RHS class H5.

Use single clumps as accents in borders or rock gardens. Groups can form ground cover or line a garden path. The blue leaves contrast with pink flowers and spring bulbs. Deer and rabbits tend to leave the plant alone. Care needs are low, and serious pest problems are uncommon. Remove dead leaves and old flower stems in spring. Divide clumps in mid-spring, or raise plants from seed. Give plants good air flow to help limit fungal disease. Rust can develop in damp, humid weather. Wet soil and poor drainage can lead to crown rot.