Johnsongrass
Grassy weed
Johnsongrass (Sorghum halepense) is a tall, aggressive warm-season perennial grass introduced to the United States as a forage crop. Gardeners and growers notice it because it spreads fast, grows head-high in a single season, and is one of the most troublesome weeds in row crops, pastures, and field edges across much of the country.
How to identify it
Look for coarse, upright stems that reach 3 to 8 feet tall, with wide, flat leaf blades that carry a distinct white or whitish midrib running down the center. The open, branching seedhead is large and loose, turning reddish to purplish as it matures. Below ground it produces thick, scaly, cream-colored rhizomes (creeping underground stems) that snap easily and store energy for regrowth. Seedlings can look grassy and innocent early on, but the fleaf midrib and spreading roots set it apart.
Where it grows
Johnsongrass grows in cultivated fields, gardens, pastures, roadsides, ditch banks, fencerows, and other disturbed, sunny ground, mostly from late spring through fall. It thrives in warm climates and rich, moist soils but tolerates a wide range of conditions. It spreads two ways at once: by abundant seed that can stay viable in the soil for years, and by an extensive network of underground rhizomes that push up new shoots several feet from the parent plant.
Why it is a problem
This weed competes hard for water, light, and nutrients, and a dense stand can sharply cut yields in vegetables, corn, soybeans, and other crops. Its vigorous rhizomes let a small patch take over an area quickly and make it very hard to remove once established. Johnsongrass can also be toxic to livestock, since stressed plants (after frost, drought, or trampling) may accumulate prussic acid (cyanide) and high nitrate levels.
How to manage it
Prevention comes first: clean soil, mowers, and tillage equipment before moving between areas so you do not carry rhizome pieces or seed to new ground. Cut or mow repeatedly through the season to stop plants from flowering and setting seed and to slowly starve the rhizomes; persistence over one or two full seasons is what pays off. In gardens, dig out small patches while removing as much of the rhizome as you can, then cover cleared soil with a thick mulch or a dense cover crop to shade out regrowth. Keeping turf, pasture, and crop stands vigorous and closely competitive gives Johnsongrass fewer openings to establish.
Commonly confused with
Young Johnsongrass is easily confused with shattercane and with fall panicum, and its seedlings can resemble corn or grain sorghum; the combination of a white leaf midrib and thick, scaly underground rhizomes helps tell it apart.
General guidance for US lawns and gardens, focused on prevention and non-chemical control. For a confirmed identification and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.