Annual Bluegrass
Poa annua · Cool-season, Annual (can be biennial/perennial in some climates), C3
Grass Family
Poaceae, Pooideae, Poeae
Grass Category
Invasive/Weed Grass, Golf Course Grass (sometimes maintained as greens turf)
Variety / Cultivar
Generic wild type (though 'Poa annua var. reptans' is the perennial biotype)
Hardiness Zones
USDA Zones 3-10; excellent cold tolerance but dies back or turns yellow in high heat/summer drought.
About This Grass
A light green, low-growing grass with a tufted habit. Key feature is its prolific seed production, often visible even at extremely low mowing heights (under 0.25 inches). Seed heads are open, pyramidal panicles, about 1-3 inches long.
Blade Characteristics
Fine to medium (2-3mm); flat or slightly folded; distinctly boat-shaped tip; light lime-green color; vernation is folded; ligule is long (up to 3mm), membranous, and white with a pointed or slightly rounded top; auricles are absent.
Root System
Shallow, fibrous root system; high thatch-forming tendency; very fast establishment from seed; poor drought tolerance due to shallow roots.
Growing Information
Origin Region
Europe and Eurasia; now naturalized globally in temperate climates
Growth Habit
Bunch-type to weakly stoloniferous; can form dense, spreading mats in low-mown areas
Sunlight & Water Needs
Full sun to partial shade; prefers moist to wet conditions and frequent watering; thrives in compacted, damp soils.
Mowing & Maintenance
0.5 to 2.0 inches (can survive at 0.125 inches on golf greens); frequent mowing required to remove seed heads; high nitrogen needs to maintain color; high maintenance level if managed as turf.
Special Characteristics
Extreme seed production allows it to dominate disturbed or over-watered areas; high shade tolerance for a lawn grass; poor traffic tolerance; low salt tolerance; highly susceptible to heat stress/wilting.
Ecological Information
Introduced/invasive in North America; provides some forage for small birds but generally considered a nuisance in managed landscapes; can outcompete native grasses in early spring due to early germination.