Johnson Grass
Sorghum halepense · Warm-season perennial, C4, highly aggressive weed in transition and southern zones
Grass Family
Poaceae, subfamily Panicoideae, tribe Andropogoneae
Grass Category
Invasive/Weed Grass, Forage Grass (with caveats), Erosion Control (incidental)
Variety / Cultivar
Not applicable (wild-type invasive species)
Hardiness Zones
USDA Hardiness Zones 6-11; heat tolerant; top growth dies back after first frost; rhizomes survive underground.
About This Grass
An upright, coarse, tall perennial grass growing in dense clumps. It can reach 3 to 8 feet if left unmowed. It features large, open, purplish panicle seed heads and a prominent white midvein on light-to-medium green leaves.
Blade Characteristics
Coarse blade width (10-30mm), flat shape with a sharply pointed tip. Light green to medium green color with a distinct, thick white midvein. Vernation is rolled in the bud. Ligule is a short, fringed membrane; auricles are absent.
Root System
Deep, aggressive fibrous roots and thick, fleshy, scaly rhizomes. Fast establishment; high thatch tendency; extremely drought tolerant and difficult to eradicate once established.
Growing Information
Origin Region
Native to the Mediterranean region; naturalized globally in tropical and temperate climates
Growth Habit
Rhizomatous (extremely aggressive spreading underground) and via prolific seed production
Sunlight & Water Needs
Full sun preferred; high drought tolerance; thrives in rich, moist soils but survives in poor, dry conditions; pH 5.5 to 7.5.
Mowing & Maintenance
Maintenance is usually control-based; if in pasture, mow before seed heads form to prevent spread. Extremely high maintenance if trying to eradicate; resistant to low height mowing as it regrows quickly from rhizomes.
Special Characteristics
Highly invasive; high wear tolerance; salt tolerant; toxic to livestock (prussic acid/cyanogenic glycosides) when stressed or after frost; excellent erosion control but crowds out all native vegetation.
Ecological Information
Introduced/Invasive status in North America; provides cover for small mammals but displaces native flora; noted as one of the world's 10 worst weeds due to competitive dominance.