Johnsongrass Identification Guide

Key Identifying Features

Johnsongrass (Sorghum halepense) is a tall, coarse, warm-season perennial grass spread by stout underground rhizomes. It is one of the most aggressive agricultural weeds in temperate regions. Recognize it by its great height, broad leaves with a conspicuous white midrib, and a large, open, branched seedhead that often takes on a reddish-purple cast.

• Tall, 5 to 8 feet (sometimes taller)
• Broad leaves with a prominent white central midrib
• Thick, scaly, creeping rhizomes with reddish spots
• Large, open, pyramidal panicle, often purplish
• Membranous ligule; lower sheaths usually hairless

Leaves & Stems

Leaf blades are long (up to 2 feet), flat, and an inch or more wide, smooth on the surface with a thick, waxy white midrib down the center, a hallmark of the species. The leaf margins are slightly rough to the touch. At the collar is a membranous, often torn ligule. Stems are stout and upright. The defining vegetative feature lies underground: thick, pinkish-white rhizomes covered in purple-brown scales, which let a single plant form large colonies. Snapping a rhizome reveals it is fleshy and segmented.

Flowers & Fruit

The inflorescence is a large, loose, much-branched panicle 6 to 20 inches long, pyramidal in outline and frequently flushed reddish-purple. Spikelets are paired, with shiny reddish-brown to blackish seeds at maturity; some bear a short bent awn. The open, airy form distinguishes it from the dense, club-shaped heads of cultivated sorghum. Flowering runs from early summer into fall.

How to Tell It Apart from Look-Alikes

• Shattercane (Sorghum bicolor): Annual with no rhizomes; if you dig and find no creeping underground stems, it is shattercane, not Johnsongrass.
• Corn seedlings: Lack rhizomes and have a different leaf base; Johnsongrass seedlings can mimic young corn but emerge from rhizomes.
• Barnyardgrass: Much shorter, annual, no ligule, no white midrib.
• Big bluestem or other natives: Lack the broad white-ribbed leaf and aggressive rhizome network.

The surest confirmation is to dig at the base: stout, scaly, spreading rhizomes plus a white-ribbed broad leaf confirm Johnsongrass.

Where You'll Find It

Johnsongrass thrives in warm, fertile, disturbed ground: crop fields, field margins, fencerows, ditch banks, roadsides, and riverbanks. It prefers full sun and moist, rich soils but tolerates a wide range. It is a serious weed in row crops across the southern and central United States and warm regions worldwide.

Quick ID Checklist

• Tall perennial grass, 5 to 8 ft
• Broad leaves with a white waxy midrib
• Thick, scaly, spreading rhizomes (dig to confirm)
• Large, open, purplish branched panicle
• Paired spikelets, shiny reddish-brown seeds
• Disturbed, fertile, sunny ground