Andropogon gerardii

Description

Andropogon gerardii is the dominant grass of the North American tallgrass prairie, a warm-season (C4) perennial bunchgrass that forms large, robust clumps reaching 1.2-2.4 m in height — substantially taller than the other "Big Four" prairie grasses with which it coexists. In Canada, it is native to southern Ontario, southern Quebec, and the southern Prairie provinces of Manitoba and Saskatchewan, with its Canadian range reaching its northern limit in the aspen parkland zone.

The foliage is blue-green to grey-green in summer, sometimes with a purplish flush at the nodes, and turns a rich maroonish-tan to copper-red in autumn — providing some of the most spectacular fall colour of any native grass. The stems are stout and erect, capable of supporting the massive inflorescences even through winter. The root system is exceptionally deep and fibrous, extending 2-3 m into the soil, which accounts for the species' remarkable drought tolerance and its role in building the deep, carbon-rich prairie soils (mollisols) of central North America.

The species is best recognized by its seedhead: a terminal inflorescence divided into three (occasionally up to seven) slender, finger-like branches that spread outward, unmistakably resembling a turkey's foot. This feature gives the plant its most memorable common name. The spikelets are arranged in pairs along each branch — one sessile, one pedicellate — with conspicuous twisted awns that catch the light. The scientific name honours French botanist Louis Gérard. Known colloquially as Big Bluestem, Tall Bluestem, and Turkeyfoot, it is the undisputed monarch of the tallgrass prairie.

Growing Conditions

Thrives in full sun and moist, well-drained soils but is remarkably adaptable. Tolerates sand, loam, and clay textures and both acidic and calcareous conditions (high calcium carbonate tolerance). While it prefers consistent moisture for optimal growth — needing more water than Little Bluestem — it is highly drought-tolerant once established due to its deep root system. Can withstand periodic flooding and high water tables. Hardy from Zone 3 to 9.

In garden settings, too much water, shade, or nitrogen fertilizer can cause the tall stems to lodge (flop over), particularly in rich soils. For best results, plant in lean soil with full exposure. Cut back, mow, or burn in late winter before new growth emerges. Never mow during the growing season, as this can kill the plant. In areas where it becomes aggressive, such as moist central plains sites, seasonal mowing can help limit spread. An essential species for tallgrass prairie restoration, but can be vigorous in favourable conditions — best used where its commanding stature can be accommodated.

Phenology

A warm-season grass that breaks dormancy late in spring, typically mid- to late May in southern Ontario, well after cool-season grasses have greened up. Vegetative growth accelerates through June and July, with flowering stalks elongating in late summer. Bloom occurs from August through November, with peak flowering in September. The distinctive three-branched seedheads open with reddish-brown to purplish tones and release pollen on warm, breezy autumn days. Seeds mature in October and November and are dispersed by wind and gravity through the winter months. Fall colour peaks in October with deep maroon, copper, and tan tones. Winter foliage and seedheads persist as structural elements through the dormant season, providing texture and movement in the winter landscape.

Ecology

Big Bluestem is the foundational species of the tallgrass prairie ecosystem. It contributed the bulk of the above-ground biomass that fuelled the frequent, low-intensity fires that maintained prairie structure against woody encroachment. Its massive root system — which can account for two-thirds of the plant's total biomass — built the deep, fertile prairie soils that later became some of the most productive agricultural land on the continent. The roots stabilize soil on slopes, improve water infiltration, and support a rich community of mycorrhizal fungi.

The species is an important larval host for grass-feeding skipper butterflies. The Delaware Skipper (Anatrytone logan) and Dusted Skipper (Atrytonopsis hianna) both use Big Bluestem as a primary larval food source. The dense clumps provide cover and nesting habitat for at least 24 species of songbirds, including Grasshopper Sparrows, Henslow's Sparrows, Sedge Wrens, and Western Meadowlarks. The seeds are consumed by sparrows and other granivorous birds through the winter. The Xerces Society recognizes Big Bluestem as providing nesting materials and structural habitat for native bees.

Historically, Big Bluestem was so abundant that early settlers described the tallgrass prairie as an ocean of grass in which a rider on horseback could be hidden. Overgrazing by cattle — to which the species is highly palatable, earning the nickname "ice cream for cows" — combined with nearly complete conversion to cropland, has reduced tallgrass prairie to less than 3% of its original extent.

Propagation

Propagate by seed or by division of established clumps during winter dormancy. For seed, collect in October and November when the spikelets readily separate from the seedhead. Seeds benefit from dry, cold stratification — store in a cool, dry place over winter and surface-sow in spring. Germination is typically robust when soil temperatures are warm. First-year seedlings invest heavily in root development and may appear modest above ground; plants reach full stature by their second or third season.

Division is best performed in early spring or late fall when the plant is dormant. Dig the entire clump and separate it into divisions using a sharp spade — the dense, fibrous root mass requires effort but divisions establish reliably. In garden settings, the centre of older clumps may die out over time; division every 3-5 years rejuvenates the plant and prevents excessive spread. The species is widely available commercially and is a standard component of prairie restoration seed mixes across eastern North America.