Plants perennial, with long‑creeping rhizomes, forming clumps. Flowering stems 35–140(–300) cm long, relatively stout and stiff, round in cross‑section, glabrous or hairy at the nodes. Leaves scattered along the stems. Leaf sheaths rounded on the back, glabrous, the ligule 2–4 mm long, a line or band of hairs (sometimes with a very short membrane at the base). Leaf blades 15–55 cm long, 3–15 mm wide, firm, arched or spreading, glabrous or hairy near the base, bluish green and often somewhat glaucous, the margins sometimes somewhat inrolled, the midvein prominent and raised on the undersurface. Inflorescences (5–)15–50 cm long, with the primary branches ascending to spreading, not spikelike, rebranched several times, the ultimate branches not appearing 1‑sided, the spikelets short‑ to long‑stalked, not or only slightly curved or angled with respect to their stalks. Spikelets (3.7–)4.0–6.0 mm long, narrowly ovate in outline, narrowed or tapered to a sharp point at the tip, glabrous. Lower glume 2.2–5.0 mm long, 2/3–3/4 as long as the rest of the spikelet, ovate, sharply pointed at the tip, 3‑ or 5‑nerved. Upper glume 3.3–6.0 mm long, elliptic, narrowed or tapered to a sharp point at the tip, strongly 7‑ or 9‑nerved. Lowermost floret sterile or more commonly staminate and with a well‑developed but not hardened palea, the lemma 3.7–6.0 mm long, elliptic, 5‑ or 7‑nerved. Fertile floret 2.4–4.0 mm long, narrowly ovate, narrowed to a blunt point at the tip. Anthers 1.3–2.0 mm long. 2n=18, 21, 25, 30, 32, 36, 54, 55, 65, 72, 90, 108. June–September.

Common nearly throughout Missouri (eastern U.S. west to Montana and Arizona; Canada, Mexico, Caribbean Islands). Bottomland and upland prairies, savannas, calcareous glades, ledges and tops of bluffs, gravel bars and banks of streams and rivers, bottomland forests, and openings of mesic to dry upland forests; also pastures, old fields, roadsides, railroads, levees, and open, disturbed areas.

Plants of P. virgatum sometimes produce inflorescences with normal branching but in which none of the spikelets mature. Such spikelets are 3.5–5.5 mm long and linear to narrowly lanceolate in outline, tapering to a very sharp point at the tip. The fertile lemmas do not develop the hardened, shiny texture characteristic of mature lemmas of this species. The spikelets appear so different from fully formed ones that such plants frequently are misdetermined, either as another species of Panicum or as some other genus, such as Agrostis.

Switch grass is a characteristic species of tallgrass prairie and dolomite glade communities, but it occurs in numerous other habitats. It provides excellent forage and hay for livestock and is an important species for warm‑season grass plantings. It also is being tested as a possible source of plant material for production of ethanol for fuel. Native variants in Missouri tend to be less than 1.5 m tall, but some of the robust genotypes (some or most apparently imported from Texas) used in forage plantings can reach nearly 3 m in height.