The Garden Life: Ornamental grasses look their best in cool weather

By Robb Rosser, Columbian Gardening columnist

Published:

 
photoRobb Rosser

As summer wanes and autumn waits in the wings, garden plants begin to change along with the weather. One of the most fascinating aspects of the summer-to-fall season is watching the metamorphosis of many structural garden plants. A group of plants that stands out at this time of year is the ornamental grasses. Most have reached their full height by the end of summer but it takes the onset of cooler weather to bring out their best qualities. Now, the stalks of ornamental grasses begin to color in burnished, autumn hues. Feathery flower spikes rise up above the foliage, swaying gracefully in the slightest breeze.

Among the ornamentals called fountain grasses, Pennisetum setaceum Rubrum is a classic for seasonal planters. Red fountain grass is at its best in full sun and average garden soil. The best way to display this beauty is to make sure that the foliage is illuminated from the side or from behind with early morning or late afternoon sun. Then the depth of color will light the plant from within in an ever-changing kaleidoscope of rich, rose reds and tawny browns. This is one grass that is difficult to overwinter in our climate, so plants are best treated as annuals and replaced each spring.

Once autumn sets in, Pennisetum orientale reaches up and out with feathery plumes of pale pink, displaying longer, purple hairs that glow in the light of the noonday sun. The arching plumes rise well above the foliage, which stays neat and attractive in a clump of dense, light green foliage. Pennisetum alopecuroides Hameln sports the classic fountain shape of the species but in a smaller form. At about 3 feet high and wide, Hameln should be planted in sweeps of three or five, to best show off the lovely white flower plumes. Little Bunny is a dwarf form, perfect for the smaller garden.

The group of ornamental grasses classified as Miscanthus is among the showiest. These are clump-forming plants that range in size from 14-feet tall to dwarf varieties measured in inches. One of the characteristics of silver grass are flower panicles that are held above the foliage and open as tassels, gradually expanding into silvery to pinkish-bronze plumes that last well into winter. Miscanthus Giganteus, also called giant silver grass, is one of the most impressive with self-supporting stems up to 2 inches thick, making it a good summer screen or hedge. Miscanthus sinensis Silver Feather is a German selection whose large, silver plumes are carried on 7-foot stems above handsomely striped foliage. With the sun behind them, they gleam like polished chrome from mid-August through the winter months.

My longtime favorites are the ornamental feather reed grasses called Calamagrostis. These sturdy, clumping grasses are Eurasian natives with feathery flower plumes that fade from purple-green to straw yellow and persist well into winter. Calamagrostis acutiflora Karl Foerster stands out with upright, flowering stems emerging from bright green leaves in early summer. It forms neat clumps of foliage and in June. The toasty-brown, feathery flower stems extend the height of the grass to 5 or more feet, forming a striking exclamation point in the garden. Despite their delicate and graceful appearance, they hold their shape through the winter.

Robb Rosser is a WSU-certified master gardener. Reach him at Write2Robb@aol.com.