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A Floridata Plant Profile #783 Panicum virgatum
Common Names: switchgrass, prairie switchgrass, tall panic grass, water panicum, wild redtop, thatchgrass
Family: Poaceae/Gramineae (grass Family)
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Grass  Perennial  Attracts Birds Drought Tolerant For Wet, Boggy Areas Provides Autumn Color

A clump of switchgrass in summer bloom.
Switchgrass in summer bloom at Northern Kentucky's Big Bone State Park.
Switchgrass is a spreading perennial grass that grows in large clumps 3-6 ft (0.9-1.8 m) tall. The sturdy, flat, glossy leaf blade may be as much as 0.5 in (1.3 cm) wide and 30 in (76.2 cm) long. The stem is round in cross section and usually has a reddish tint. The inconspicuous flowers, which have reddish-purple anthers, are borne in open 10 in (25.4 cm) panicles. They produce shiny teardrop shaped 1/8 in (0.3 cm) seeds. On Midwestern prairies and bottomland sites, switchgrass develops long rhizomes (underground stems) that grow horizontally to interlace and form a thick, dense sod.

'Heavy Metal' switchgrass
The cultivar Panicum virgatum 'Heavy Metal' is a popular garden plant - seen here at the Atlanta Botanical Garden.

On upland sites and in the southeast, switchgrass grows as a bunchgrass. The roots of switchgrass may reach depths of 10 ft (3.1 m) or more. Switchgrass is a warm season perennial that waits until summer to put on its top growth. The rhizomes are in active growth from late winter through mid-spring, but the top stays dormant until the soil warms up. Switchgrass typically turns a nice pale yellow in the fall, but some cultivars have been selected for more striking colors. 'Shenandoah' has outstanding burgundy foliage - the leaves start showing dark red tones by midsummer and are fully colored by early fall. 'Dallas Blues' has bluish foliage. 'Heavy Metal' is a stiffly upright switchgrass characterized by metallic lavender-blue foliage with a waxy white bloom; it turns bright yellow and displays dark burgundy seedheads in the fall. 'Rehbraun' is a 3-4 ft (0.9-1.2 m) cultivar with foliage that turns red in the late summer. 'Haense Herms' has pink flowers and dark red autumn leaves.

Switchgrass is common in Midwestern prairies and in openings and savannas throughout the eastern United States. It is one of the co-dominant grass species of the original tallgrass prairie.

This is the switchgrass cultivar called 'Rotstrahlbusch'.
This is the switchgrass cultivar called 'Rotstrahlbusch' photographed at the Atlanta Botanical Garden.
Switchgrass grows on a wide variety of soils, but likes deep sandy loams best. It does poorly on heavy soils, although it tolerates moderate soil salinity and pH levels ranging from about 4.5 to 7.6. Once a stand has been established, it will benefit from fertilization, but nitrogen should be applied only sparingly early in the growing season and never on very young plantings, lest it encourage competition from cool-season grasses. Switchgrass grows best in association with site-adapted mycorrhizal fungi. It may take many years for mycorrhizae and associated beneficial soil microbes to become well established on a newly planted site and this process may be inhibited by application of nitrogen rich fertilizers. Switchgrass can be mowed or grazed down to about 8 in (20.3 cm) in the winter, but the stubble is important for winter insulation and should not be cut shorter than that in cold climates. This species evolved with fire and does best when burned occasionally. Switchgrass typically survives fire by regrowing from protected underground rhizomes, but the vigor of the new growth depends upon the season and intensity of the fire, and whether it is of the more fire resistant sod-forming type with rhizomes several inches below the soil surface, or the more sensitive bunchgrass type with rhizomes growing up into elevated tussocks. Switchgrass should be burned just before it begins growing in the spring. A fire every 3-5 years is recommended.
Light: This is a grass that will grow in partial shade.
Moisture: Switchgrass is not particular about moisture. It is found in dry, mesic, and wet habitats, but grows most luxuriantly in bottomlands. It is tolerant of spring flooding but not of persistent high water tables.
Hardiness: USDA Zones 4 - 9. Switchgrass can tolerate temperatures down to -30ºF ( ºC).
Propagation: Switchgrass typically produces heavy crops of seed, but only a small percent are viable. Seeding at a rate of 2-10 lbs./acre is often recommended, but it may take many times this amount to produce a dense stand. The seeds drop from the plants within a few weeks after ripening, but require dormancy at winter temperatures before they will germinate. Switchgrass seeds must be firmly planted 1/4-1/2 in (0.6-1.3 cm) deep. They begin to sprout when the soil temperature reaches 68ºF (20ºC)in the spring. If weed competition is controlled, the seedlings may be 1 ft (0.3 m) tall with roots reaching nearly 3 ft (0.3 m) into the soil by midsummer. The plant's early growth will be directed into the roots, so full foliage development should not be expected until at least the third year. Seedlings bloom the first or second year. Plants may be propagated by division of new shoots, though it is usually a challenge to break apart the masses of tough tangled roots. Transplants may be set out either in the spring or the fall.

The switchgrass cultivar 'Sheire'.
This is the switchgrass cultivar 'Sheire' growing at the Cincinnati Zoo and Botanical Garden.
Switchgrass provides good forage for cows, horses, and sheep in the spring and early summer, but nutrient content declines and the leaves become too coarse and tough to be palatable later in the season after the seedheads develop. Pastures must be managed carefully, however, because this species is a "decreaser" that dies out where overgrazed during the growing season. Switchgrass is often used in revegetation, restoration, and erosion control projects. It also is being studied as a potential energy biomass crop.

Switchgrass is essential for wildflower meadows intended to mimic North American prairies. It can be used to add fall color to naturalistic borders and woodland-edge gardens. It is also a great wildlife plant. Switchgrass holds up well under heavy snow and provides good fall-winter cover for rabbits and other small mammals, ducks, pheasants, and quail. The seeds are eaten by turkeys, pheasants, quail, doves, and songbirds. Switchgrass prairies are favored nesting sites for pheasants, quail, greater prairie chickens, and sharp tailed grouse. White tailed deer and other native ungulates paw up the rhizomes for winter survival food.

Though young plants need protection from weeds, switchgrass becomes a very aggressive competitor as it gets older. Do not plant it in meek company! Early hunters avoided patches of this grass when cutting buffalo meat because the tiny spikes would get embedded in the meat. These sharp spikelets also have an annoying inclination to creep inside one's pants legs.

Linda Conway Duever 08/27/00; updated 05/28/01, 12/16/03

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