Kentucky Bluegrass
Poa pratensis · Cool-season, Perennial, C3 grass
Grass Family
Poaceae, subfamily Pooideae, tribe Poeae
Grass Category
Lawn/Turf Grass, Sports Turf, Golf Course Grass
Variety / Cultivar
Midnight (known for dark blue-green color, excellent density, and disease resistance)
Hardiness Zones
USDA Hardiness Zones 3 to 7, tolerates cold winters well (down to -40°F or lower) but struggles with extreme summer heat and humidity in the deep southern US transition zone. Enters winter dormancy when temperatures drop consistently below freezing.
About This Grass
Forms a dense, fine-to-medium textured turf with an attractive blue-green to dark green color. Height when unmowed reaches 18 to 24 inches, but maintained lawn height is typically 1.5 to 2.5 inches. Develops open panicle seed heads at maturity during late spring to early summer.
Blade Characteristics
Medium-fine width (2 to 4 mm), flat to slightly folded shape with characteristic boat-shaped (prow-shaped) tips. Color is vibrant blue-green. Vernation is folded in the bud. Ligule is short and membranous. Auricles are absent. Distinct parallel veins visible on the upper surface with a prominent midrib.
Root System
Moderately deep fibrous root system combined with extensive, aggressive rhizomes. High thatch-forming tendency under high fertility and moisture. Slow to moderate establishment speed from seed, but excellent long-term self-repair and wear recovery.
Growing Information
Origin Region
Europe and Northern Asia, widely naturalized and cultivated across North America and temperate regions worldwide; performs best in northern temperate climates
Growth Habit
Rhizomatous (spreading aggressively via underground stems), forming a dense, uniform, wear-resistant sod and turf mat
Sunlight & Water Needs
Requires full sun (minimum 6-8 hours daily) for optimal growth, though some cultivars tolerate light partial shade. Moderate to high water needs; goes into summer dormancy (turning brown) during severe drought, but recovers quickly when moisture returns. Prefers well-drained, fertile loamy soils with a pH of 6.0 to 7.0.
Mowing & Maintenance
Ideal mowing height is 1.5 to 2.5 inches. Mowing frequency is high during peak spring and autumn growth periods (weekly or more). High fertilization needs (3-5 lbs N per 1000 sq ft annually). Requires regular dethatching and core aeration due to dense thatch production. High maintenance level overall.
Special Characteristics
Excellent wear tolerance and superior ability to self-repair due to aggressive rhizomes. Good cold tolerance and winter color retention compared to warm-season grasses. Moderate tolerance to foot traffic, but susceptible to diseases like summer patch, dollar spot, and leaf spot under stress.
Ecological Information
Introduced species in North America. Provides good soil stabilization, erosion control, and dense surface cover. Commonly blended with Perennial Ryegrass and Fine Fescues to improve disease resistance, establishment speed, and shade adaptability in turf seed mixes.