Annual Bluegrass
Poa annua · Cool-season winter annual (occasionally short-lived perennial), C3
Grass Family
Poaceae, Pooideae, Tribe Poeae
Grass Category
Invasive/Weed Grass, Golf Course Grass (Greens)
Variety / Cultivar
Common (non-specified variety); includes biotypes such as Poa annua var. annua (annual) and POA annua var. reptans (perennial)
Hardiness Zones
USDA Zones 3-11 (ubiquitous); poor heat tolerance, enters dormancy or dies above 85°F (30°C).
About This Grass
A low-growing, tufted grass characterized by its prolific seed head production even at very low mowing heights. It appears light lime-green compared to darker turf grasses. It often dies out suddenly during summer heat, leading to brown patches as seen in the foreground of the image.
Blade Characteristics
Fine to medium (2-3mm), flat or slightly folded, with a distinct boat-shaped tip. Blades are soft, apple-green to lime-green in color. Vernation is folded in the bud; ligule is membranous, long, and white; auricles are absent.
Root System
Very shallow, fibrous root system; poor heat and drought tolerance; establishes rapidly from seed bank in soil.
Growing Information
Origin Region
Europe; now naturalized globally in temperate climates and high-elevation tropics
Growth Habit
Bunch-type to slightly stoloniferous; forms dense, low-growing light-green clumps or mats
Sunlight & Water Needs
Partial to full sun; prefers moist to over-watered conditions and compacted soils; low drought tolerance.
Mowing & Maintenance
Highly adaptable to mowing heights from 0.1 inch (golf greens) to 3 inches. Requires high maintenance to eradicate or high inputs (frequent irrigation/fungicide) to maintain as a surface.
Special Characteristics
Extremely high seed production; seeds can germinate year-round in cool moist conditions; high shade tolerance; low wear tolerance.
Ecological Information
Introduced/Invasive status in lawns; serves as a food source for some waterfowl but generally considered a major nuisance weed in managed turfgrass and agricultural settings.