Ornamental grasses are garden mainstays, and with good reason. Their graceful silhouettes add softness and texture to mixed perennial borders, shrub borders, and backyard meadows. They're carefree growers, but to look their best they need periodic shearing or thinning. Without it they become an unsightly mix of new and dead growth.

Landscape designer Michelle Comeau of Carmel, California (831/620-0111), uses the techniques at far right to cut back grasses for her clients. Her best advice: Match the right method to the types of grasses you grow, whether warm-season or cool-season kinds, and trim at the appropriate time.

Deciduous (warm-season) grasses' foliage turns brown in fall before plants go dormant. Their billowy silhouettes are majestic in winter, so wait to cut them back until late winter or early spring, when new growth appears from the base; plants will regrow quickly. (In areas of high fire risk, cut back when foliage turns brown.) If necessary, also divide large, old clumps of grasses. Dig out the plant, then use a saw or shovel to cut the rootball in half or in quarters vertically; don't dislodge the soil around the roots. Replant divisions immediately.

Evergreen (cool-season) grasses have foliage that generally stays green through winter, though cold snaps can kill off top growth. Some types, such as feather reed grass, are semievergreen. Cut these grasses back in late winter or early spring. Divide old clumps in fall, winter, or spring.

WHAT TO DO NOW

Deciduous grasses. Using sharp hedge shears or pruning shears, cut off one section of foliage at a time. Work through the plant laterally, leaving only a small mound. Shear small grasses (those 3 ft. and under) down to 1 1/2 to 3 inches tall, larger grasses (3 to 6 ft.) down to 4 to 6 inches tall.

Common types include eulalia (Miscanthus), fall-blooming reed grass (Calamagrostis brachytricha), fountain grass (Pennisetum orientale 'Karley Rose'), and Japanese forest grass (Hakonechloa macra).

Evergreen grasses. Selectively cut out dead growth with pruning shears or comb out dead growth with your fingers. Prune off brown tips or cut plants back by one-third to renew and shape them. Carex texensis, C. tumulicola, and Festuca mairei can be cut back by two-thirds.

Some commonly grown evergreen grasses are blue oat grass (Helichtotrichon sempervirens), feather reed grass (Calamagrostis x acutiflora 'Karl Foerster'), rush (Juncus), and sedge (Carex).