'Karl Foerster' feather reed grass
Several exciting new ornamental grasses have come into our gardens the last few years, but none with the beauty, versatility, and reliability of feather reed grass, also known as Calamagrostis acutiflora 'Karl Foerster'.
This tall and narrow grass is believed to be a natural hybrid of C. epigejos and C. arundinacea, both natives of Europe and Asia. The noted German nurseryman, Karl Foerster, discovered the plant in the Hamburg Botanical Garden. He listed it in has 1939 nursery catalog, and included it in his 1950 garden book, The Use of Grasses and Ferns in the Garden. From there it spread around Europe until in 1964 it was brought from Denmark into the U.S.
Leaf blades are 2 to 3 feet long and a deep, shiny green. Loose, feathery flowers atop 5-foot stems appear in June and are initially light pink in color. As the seed heads mature, they become very narrow and turn a golden tan color that lasts through the fall. One of the distinguishing and highly regarded features of 'Karl Foerster' compared to other varieties is its narrow and upright growth. At only 18 inches wide and up to 5 feet tall, a grouping creates a dramatic vertical element in gardens.
The plant is fully deciduous in cold winter areas, but semi-evergreen in mild winter climates. Leaves emerge early in spring and last until early winter.
Unlike many common ornamental plants from other continents, the seeds of 'Karl Foerster' are sterile. After nearly 40 years in American gardens, it has never become an invasive pest.
Where and how to grow
'Karl Foerster' grows well in most North American gardens. Hardy throughout USDA Zones 4 through 9. 'Karl Foerster' is a cool-season grass meaning it grows best at temperatures near 70oF, and the best time to plant is spring in the North; fall in the South and West. The plant does suffer in the heat and humidity of an eastern zone 9 summer.
Plant in full sun to partial shade, in well-drained soils. Moist soil and regular rain or irrigation are preferable, but the plant will tolerate heavier clay soils and drier sites.
To grow to their maximum 5-foot height, fertilizer is required. Use about 1 pound of a 10-10-10 fertilizer per 100 square feet. Low fertility is not a problem, but will result in shorter plants.
'Karl Foerster' is usually free of serious disease or insect problems although a foliar rust disease may appear in particularly wet summers and in situations with poor air circulation. Browsing deer don't bother it. Little maintenance is required except to cut back the stems to about 6 inches in late winter or early spring. In areas with mild winters the foliage may remain evergreen.
Some call the plant "metamorphic" for all the different stages it passes through in a season. Others have referred to it as the "perpetual motion grass" for its ability to catch and give motion to the slightest breeze.
Use 'Karl Foerster' as an individual specimen or small clump to provide a strong vertical accent, or mass a row to create a very fast growing, 5-foot high screen. It also serves well in containers and will survive most winters unprotected as far north as zone 6.
Naturally floral designers love 'Karl Foerster' for its use in fresh or dried arrangements. Stems cut before the flowers mature will last for months in an arrangement while maintaining the golden tan color. In heavy rain or wind the stems will dip and droop in all directions but return to vertical as soon as the storm passes.
A combination of 'Karl Foerster' feather reed grass with various other perennials makes a dramatic effect in the landscape. Consider combinations with late summer and fall-blooming perennials blooming perennials such as Coreopsis, Echinacea, Liatris, and Rudbeckia.
Given all this attributes, it's easy to see why 'Karl Foerster' feather reed grass is one of the most popular ornamental grasses year after year, and why the Perennial Plant Association named it Perennial of the Year.
Michael MacCaskey is the editorial director at National Gardening Association.