Helictotrichon sempervirens, or blue oat grass, is a cool-season, clump-forming grass with steel-blue leaves. This is an award-winning plant that would look great in any garden. It received the Royal Horticultural Society’s Award of Garden Merit in 1993 and was chosen for Great Plant Picks in 2004. The tidy, bristly mounds create an eye-catching decorative plant. It resembles blue fescue (Festuca ovina glauca cultivars), but grows higher and has thicker blades.
Native to central and southwestern Europe, this perennial grass is hardy in zones 3 or 4-8.The long, wiry leaves on arching stems are about ½ inch wide and taper to a fine point. Under optimal conditions it grows about two feet tall and three feet wide. Graceful flower plumes grow vertically from the center of the plant. Pale blue flowers bloom on beige, one-sided panicles in midsummer. It often does not consistently produce the attractive, arching four foot flower stems in more northern areas where there is a shorter, cooler growing season. The leaves turn light brown in autumn and persist through the winter.
This small ornamental grass has many landscape uses, with a color and texture few plants have. It makes a nice addition to the perennial border, particularly as a contrast to green-leaved plants. Use it as a single accent plant in the smaller garden or rock garden, grow it in masses for a fine-textured drift, or try it in a container. Blue oat grass makes a nice row along a walkway, or can be added to the front of a shrub border. It combines well with Russian sage (Perovskia), Salvia x sylvestris ‘Mainacht’ (‘May Night’), blanketflower (Gaillardia), Sedum ‘Autumn Joy’ and other, more upright ornamental grasses. Use it to echo the blue foliage or flowers of blue spruce, blue junipers or blue-flowering perennials such as Campanula, lavender (Lavendula), or blue mist spirea (Caryopteris). For a more dramatic effect, try combining it with plants with deep maroon leaves.
Plant blue oat grass in full sun. Well-drained soil is essential for winter survival. Although it prefers a moist soil, it will tolerate sandy as well as heavy clay soils – as long as it does not remain too wet in winter. Evergreen in milder climates, the leaves die back in Wisconsin winters; use a rake to remove the old foliage or cut back close to the ground in late winter. This plant has no significant insect pests or diseases other than crown rot that occurs in poorly drained soils.
There are a few cultivars:
- ‘Sapphire’ has finer blades that are slightly smaller and bluer than the type.
- ‘Saphirspudel’ (‘Sapphire Fountain’) is a finely textured, semi-evergreen selection from Germany.
In the spring, divide blue oat grass or start from seed. Sow new seed in late summer, maintain in a cold frame throughout the winter, and they should germinate in spring.