Kentucky Bluegrass (Poa pratensis L.)

Common Name: Kentucky Bluegrass

Scientific Name: Poa pratensis L.

Synonym: Poa pratensis L. ssp. alpigena (Fries ex Blytt) Hiitonen; Poa pratensis L. ssp. colpodea (Fries ex Blytt) Tzvelev; Poa pratensis L. ssp. pratensis

Known as smooth-stalked meadow grass in England.

Family: Poaceae

Tribe: Poeae

Origin: Native or EuroAsia, with many species having worldwide distribution.

Time of introduction:
Introduced to USA by earliest settlers (circa 1600) as an agronomic crop and livestock feed.


Description:

Kentucky bluegrass is a cool-season perennial. It grows well in central Kentucky on the high phosphate limestone soils of that region. However, it is a cool season grass that also grows well in northcentral and northeastern US and Canada. Kentucky bluegrass has open panicles that are pyramidal or oblong-pyramidal in shape. Leaves are folded in the bud shoot with blades that are parallel-sided and terminate in a boat-shaped tip that is characteristic of the Poa. Its sheath is flattened and smooth and has overlapping margins. Kentucky bluegrass tolerates a wide range of soils and tolerates flooding, but not a high water table. It is neither acid- nor alkali-tolerant, but survives in a pH range of 5.8 to 8.2. Kentucky bluegrass is not as high yielding as some other cool-season grasses but has many favorable qualities including its vigorous creeping growth via rhizomes, tolerance to close grazing, and high palatability. Grubs cause the most serious damage to bluegrass pastures. Control of insect damage in bluegrass pastures is best achieved through good grazing and cultural management. Renovation with legumes has also reduced grub damage.

Life cycle (annual/biennial/perennial):
Perennial.

Growth habit & Regrowth type:
Low growin. Spreads by slender, extensive, determinate rhizomes.

Invasive potential:
Moderate; spreads easily by rhizomes and has the ability to adapt to a wide range of environmental conditions. It is easily spread by seed, often introduced into areas in hay bales of other species or by grazing animals that have eaten the seed and later defecate somewhere else. Owing to its short stature it is easily crowded out by taller plant species where grazing or cutting is infrequent and/or a tall stubble height is left, but it may remain as understory plant until shaded out completely.

Persistence:
Highly persistent due to extensive rhizomes, high viable seed production that often escapes harvest and removal, and inherent adaptability of apomictic lines.

Identification:

Image Gallery: The OSU Forage Information System contains an Image Gallery that includes Kentucky Bluegrass photographs and drawings useful in identification. The URL for the gallery is: http://forages.oregonstate.edu/main.php?PageID=241

The direct URL for Kentucky Bluegrass is: http://forages.oregonstate.edu/main.php?PageID=178&SpecID=3

Inflorescence: Open panicles are pyramidal or oblong-pyramidal in shape, usually 4 to 8 inches in length (10-20 cm). Kentucky bluegrass inflorescence image.

Spikelets: Glumes at the base of spikelets are shorter than the lowermost lemma. Spikelets contain 3 to 5 florets.

Seed: Slender, tan with cottony pubescence ("cobwebs") on lemmas. Kentucky bluegrass seed image.

Stem: Flowering culms are 11 to 47 inches (30-120 cm) long.

Leaf: Leaves are folded in the bud shoot. Blades are 2 to 4 mm wide and 5 to 15 cm long, parallel-sided and terminate in a boat-shaped tip that is characteristic of the Poa. Sheath is flattened and smooth and has overlapping margins. Kentucky bluegrass leaf image.

Collar: Collar is broad and divided. Short, truncated, membranous ligules are 1.5 mm long. Auricles are absent. Kentucky bluegrass collar image.

Root: Rooting is shallow, and roots and rhizomes may be matted in mature stands. Rhizomes form mostly in late spring after inflorescences have formed. Kentucky bluegrass root image.

Physiology and growth period:
Cool-season (C3) grass, slow to establish due to 14-day germination time and long juvenile stage. Once established it rapidly colonizes meadows, pastures, and turf through extensive rhizome production. Due to need for ample soil water availability and cool conditions, spring and early summer plus a period in the fall are times of greatest growth rate. It reaches anthesis 10 or more days earlier than orchardgrass, smooth bromegrass, and timothy.

Reproduction:
Tillers of a critical size vernalize under periods of short days and low temperatures producing flowering culms with a panicle inflorescence. It is predominantly an asexual reproducing plant with an apomictic form of reproduction.

Quality/anti-quality factors:
Forage can be high or low quality, because if sampled early, Kentucky bluegrass will be more mature than other species. However, if properly managed, quality is excellent in pastures, with high crude protein content and high digestiblity. Further, digestibility declines less rapidly than other cool-season grasses.

Kentucky bluegrass has no known problems arising when livestock or wildlife graze the herbage. Some ergot is found, but it proves to be of little consequence.

Photographs/drawings:


Adaptation:

Well adapted to the humid, temperate region of the US. It has a low tolerance to drought but recovers well from it. Soil tolerances allows growth on a wide range of soils.

Suitability zones:
Ubiquitous in permanent pastures in humid, temperate regions of the US, occuring in every state and extending into Canada. Tolerates a wide range of environments from 30 to 83 degrees N latitude, from sea level to 4,000 meters (13,120 feet). Well adapted to the humid, temperate region of the US. Naturalized throughout entire range of adaptation.

Map:

Tolerances:

Quantitiative Table:

July
Max Temp (C)
Jan
Min Temp (C)
Annual
Precip (mm)
Soil pH Soil Drainage
(categories)
Soil Salinity
(mmhos/cm)
Low High Low High Low High Low High Low High Low High
Well Adapted 9999 31 -24 9999 425 1400 5.75 7.0 MWD WD 9999 3
Moderate 9999 31.5 -26 9999 400 1425 5.5 7.25 SPD WD 9999 4
Marginal 9999 32 -28 9999 375 1450 5.25 7.5 PD WD 9999 6
1. For the High values for January Minimum temperature and Annual Precipitation: "9999 is entered to indicate no limit to the high values for this tolerance category."
2. For Soil Drainage categories, " Abbreviations are used for Soil Drainage categories: VPD (very poorly drained), PD (poorly drained), SPD (somewhat poorly drained), MWD (moderately well drained), WD (well drained), SED (somewhat excessively drained), ED (excessively drained)."

Climate: Kentucky bluegrass is winter hardy, occurring at all altitudes below alpine regions. It has a January mean minimum temperature tolerance of approximately -4 F (-20 C) and a July mean maxium temperature limit of 89 F (32 C). Minimum mean annual precipitation is approximately 18 to 25 inches (450-600 mm). It has a low tolerance for drought.

Soils: Kentucky bluegrass is adapted to a wide range of soils, but persists better on well-drained, medium-textured soils. It is neither acid- nor alkali-tolerant, but survives in a pH range of 5.8 to 8.2. It tolerates periodic flooding, but not a high water table. Its a maximum salinity level is 6 mmhos/cm, but it grows best with a level of less than 4 mmhos/cm.

Grazing Management: Kentucky bluegrass is highly resistant to grazing because its growing points remain near the ground throughout the growing season and has a low ratio of reproductive to vegetative stems. Begin grazing when 5 inches (12.5 cm) to a minimum of 1.5 to 2 inches (3.75-5.0 cm).

Turf Management:
Mowing
Begin mowing young grass when it grows above a 2-inch (5 cm) cutting height. Either rotary or reel type mowers may be used but blades must be sharp and reels properly adjusted to prevent pulling up young seedlings. The initial cutting should be at a 2-inch (5 cm) height. Subsequent mowings should be frequent enough so that no more than one-third of the leaf is removed at each mowing. At a 2-inch (5 cm) mowing height the grass needs mowing before it reaches 3 inches (7 cm). Weekly mowing is usually satisfactory at the 2-inch (5 cm) mowing height. At lower mowing heights more frequent mowing is required.

Variety selection

Pests: Diseases: Common diseases of bluegrass include leaf spot and crown, root, and rhizome rots; leaf, stem, and stripe rusts; stripe smut; and powdery mildew. Fungicides are commonly used to control diseases in seed fields and for turf, but are too costly to apply to pastures.

Pests: Insects: Grubs cause the most serious damage to bluegrass pastures. Adults of Japanese bettele, May beetles, green June beetle, northern masked chafer, and European chafer lay their eggs in thin overgrazed pastures and their larvae feed on roots and rhizomes. Cutworms and army worms and several other species feed on top growth. Control of insect damage in bluegrass pastures is best achieved through good grazing and cultural management. Renovation with legumes has also reduced grub damage.

Pests: Nematodes: None reported.


Cultivars:

For turf use, over 100 cultivars (varieties) of Kentucky bluegrass have been developed during the past 25 years. Some varieties tolerate southern climates better than others (Adelphi, Baron, Fylking, Glade, Midnight, Ram I, Vantage, Victa and Warrens A-34), some have moderate shade tolerance (Bristol, Glade, Nugget and Touchdown), and some tolerate closer mowing (Adelphi, Bristol, Ram I and Touchdown). For tufgrass use in the transition zone, select a blend of about 3 varieties to increase potential for success. Many of these grasses differ in their degree of susceptibility to leaf spot diseases and Fusarium blight, both being troublesome in the transition zone. A blend of several varieties will usually appear superior to a single variety since all varieties are usually not affected by adverse conditions at the same time or to the same degree (from Duble, 2004).

Forage Information System Cultivar Database


Establishment:

Kentucky bluegrass can be seeded year around, but best results are obtained in the spring and fall. Germination is slow (approximately 14 days) and new seedings require light, frequent watering (2 to 3 times per day for the first 2 weeks). After seedling emergence, watering frequency can be reduced.

Seeding rate:
For turf use, plant 2 to 3 pounds per 1,000 sq. ft. of lawn (87-130 lb/a; 97-146 kg/ha). Lower seeding rates require much longer to develop a cover, particularly where seed are broadcast over the soil surface. Where seeds are drilled into the top inch of soil, lower seeding rates can be used.

For forage, when seeded alone, use 6 to 12 lbs/acre (6.75-13.5 kg/ha).

Seeding depth:
Seeds may be broadcast and rolled or cultipacked to ensure good seed-soil contact. Or, when drilled, seed to a depth of 0.125 to 0.25 inches (0.32-0.64 cm).

Fertilization and liming:
For forage production, in Kentucky the recommendation is to fertilize to maintain high phosphate and potash soil test levels and lime for a pH of 6.4. Clovers (especially white clover) are very compatible with Kentucky Bluegrass and is capable of supplying the nitrogen needed by the grass. If clover or other legume is not present, nitrogen fertilizer should be applied in late winter (up to 80 lbs/acre; 90 kg/ha in February or March) and again in late summer (50 to 60 lbs/acre; 56-67 kg/ha in August).

For turf, nitrogen requirements of Kentucky bluegrass are much higher during the establishment year than during subsequent years. The grass will respond to 5 to 6 pounds of nitrogen per 1,000 square feet (217.5 lb/a; 243.6 kg/ha) the first year; whereas, 2 to 3 lb/1,000 sq.ft. (87-130.5 lb/a; 97-146 kg/ha) are adequate for maintenance after the first year. During summer months Kentucky bluegrass will burn if too much soluble nitrogen is applied at one time or if it is not watered in immediately after application. Slow release nitrogen sources can be applied in larger amounts and less frequently.

In alkaline soils Kentucky bluegrass often develops iron chlorosis, a yellowing between the veins of young actively growing leaves. Color can be quickly restored with a foliar application of ferrous sulfate at 2 oz. (56.8 g) per 1,000 sq. ft. (5.5 lb/a; 6 kg/ha) or another iron source at recommended rates. Iron chlorosis is aggravated by high levels of phosphorus in the soil. Where iron chlorosis is a problem, phosphorus fertilization should be kept to a minimum.


Uses:

Forage (as pasture), turf, soil and water conservation, roadside cover.

Seed crop:
Prior to 1950, most of the Kentucky bluegrass seed was produced in Kentucky, westward into eastern Kansas, in southern Iowa, Wisconsin, Minnesota, and eastern North Dakota. Currently more than 90% of the bluegrass seed produced in the US is grown in contiguous counties of Idaho and Washington and in regions of west central and eastern Oregon. A smaller amount of seed is produced in northwest Minnesota.

Seed yields under irrigation are usually 500 pounds per acre (560 kg/ha) or better.

Forage:
For forage, Kentucky bluegrass is used predominantly as a pasture grass in north central and noreastern states. Due to its low growth habit and rhizomatous nature, it tolerates heavy grazing or frequent cutting. It is seldom used for hay or silage. Compared to other cool-season grasses, it has low productivity in summer and its early maturity results in low quality when harvest late. It has excellent compatability with white clover and birdsfoot trefoil.

Erosion Control/Conservation:
Often a component of mixtures used for soil, water, and wind erosion control. In 'unimproved' ground cover conditions, Kentucky bluegrass may compose 80% of the species, including native prairie sites which would otherwise have open spaces and be subject to weed invastion. It can also be used as an effective filter grass sod for waste water applications.

Wildlife habitat and feed:
Kentucky bluegrass is grazed by mule deer, elk, antelope, and moose. Grazing by big game (mule deer and elk) is reported on a Douglas fir-ponderosa pine-Kentucky bluegrass community. Kentucky bluegrass also contributes a small portion of the diet of bighorn sheep in British Columbia.

Turf:
Most widely used turf species in the northern USA. It has soft, medium to fine-leaf texture, high shoot densiry, dark green color, and good persistence. Due to to its extensive rhizomes it is used in sod production and as a component of many mixtures.


Economic value:

Seed:
In Oregon, Kentucky bluegrass is grown for seed on approximately 18,000 acres (7,300 hectares). Seed production is approximately 18 million pounds (8 million kg) with a value of nearly $14 million.

Region(s) of production (states): Present day seed production is localized in northern Minnesota and the Pacific Northwest.

Forage:
Kentucky bluebgrass contributes to 16.5 million hectares (40.8 million acres) of pasture in the north central and noreastern sections of the USA.

Soil and water conservation:
Kentucky bluegrass is used in many seed mixtures that are planted to control soil erosion and filter water prior to return to rivers and lakes.

Turf:
Kentucky bluegrass is the most widely used turfgrass in the midwestern and northeastern US. It is used on athletic fields, home lawns, golf course fairways, parks, cemeteries.


References:

  1. Balasko, J.A., G.W. Evers, and R.W. Duell. 2003. Forages: Volume 1. An Introduction to Grassland Agriculture: Bluegrasses, Ryegrasses, and Bentgrasses. 5th Ed. Iowa State Univ. Press. Ames, Iowa. 15-16:357-371.
  2. Cool-Season Forage Grasses. 1996. American Society of Agronomy monograph No. 34. ASA, CSSA, SSA, Madison, WI. 841 pp.
  3. Duble, R.L. 2004. Kentucky bluegrass. Texas Cooperative Extension. College Station, Texas. Available at http://aggie-horticulture.tamu.edu/plantanswers/turf/publications/bluegrass.html (verified 12 June 2004).
  4. Fermanian, T.W., and T.B. Voigt. 2004. Turfgrass Species: Kentucky Bluegrass. Turfgrass Program, Univ. of Illinois. Urbana, IL. Available at http://www.turf.uiuc.edu/ (verified 12 July 2004).
  5. Forage Information System [Online]. 2004. Oregon State University. Available at http://forages.oregonstate.edu/main.cfm?PageID=172&SpecID=3 (verified 12 July 2004).
  6. Forages: An Introduction to Grassland Agriculture. 2003. Vol. 1. 6th Ed. Iowa State Univ. Press. Ames, Iowa. (See: Kentucky bluegrass in the 'Compendium of Common Forages' in middle of book.)
  7. Harrison, R.D., N.J. Chatterton, R.J. Page, M. Curto, K.H. Asay, K.B. Jensen, and W. H. Horton. 1996. Competition, Biodiversity, Invasion, and Wildlife Use of Selected Introduced Grasses in the Columbia and Great Basins. Utah State Univ. Res. Rep. 155.
  8. Jacques, D. 2002. The identification of certain native and naturalized grasses by their vegetative characters. Canadian Agriculture Library (CAL) [Online]. Available at http://www.agr.gc.ca/cal/epub/762e/762_toc_e.html(verified 12 July 2004).
  9. Hartley, W. 1961. Studies on the origin, evolution, and distribution of the Gramineae. IV. The genus Poa L. Aust. J. Bot. 9:152-161.
  10. Purdue University Forage System. 2004. Forage ID section: Kentucky Bluegrass. Purdue University Agronomy Extension. West Lafayette, Indiana. Available at http://www.agry.purdue.edu/ext/forages/publications/grasses/k_bluegrass.htm (verified 12 July 2004).
  11. Seed Agronomy Extenion Web Segment [Online]. 2004. Oregon State University. Corvallis, Oregon. Available at http://cropandsoil.oregonstate.edu/seed-ext/ (verified 12 July 2004).
  12. Smoliak, S., R.L. Ditterline, J.D. Scheetz, L.K. Holzworth, J.R. Sims, L.E. Wiesner, D.E. Baldridge, and G.L. Tibke. 2004. Kentucky Bluegrass. Montana Interagency Plant Materials Handbook. Animal and Range Sciences Extension Service. Bozeman, MT. Available at http://animalrangeextension.montana.edu/Articles/Forage/Species/Grasses/Kentucky-bluegrass.htm (verified 12 July 2004).
  13. USDA, NRCS. 2004. The PLANTS Database, Version 3.5 [Online]. National Plant Data Center, Baton Rouge, LA. Available at http://plants.usda.gov/cgi_bin/plant_profile.cgi?symbol=POPR (verified 12 July 2004).
  14. Wedin, W.F., and D.R. Huff. 1996. Cool Season Forage Grasses: Bluegrasses. Agronomy Monograph No. 34. ASA, CSSA, SSSA; Madison, WI. 665-690.


Authors:
David B. Hannaway, Daniel Myers, and Christina Larson; Oregon State University
Marc Cool, Barenbrug - USA

Document creation:
04 June 2004

Last update:
13 August 2004

Reviewers:
Monroe Rasnake, University of Kentucky
James B. Cropper, Natural Resource Conservation Service (NRCS)

Review date:
02 June 2004 (Rasnake)
22 June 2004 (Cropper)