To Grass Species


Kentucky Bluegrass (Poa pratensis)

Plant Species
From Montana Interagency Plant Materials Handbook *
 By
S. Smoliak, R.L. Ditterline, J.D. Scheetz, L.K. Holzworth, J.R. Sims, L.E. Wiesner, D.E. Baldridge, and G.L. Tibke

Kentucky bluegrass is a native of the Old World, occurring over much of Europe and Asia, and was probably brought to this country by early colonists soon after 1600. This plant has been described as having the widest distribution of any plant in the temperate portions of the northern hemisphere. It is naturalized in most states, and is seeded extensively for lawn and pastures. Although it is used principally for lawns, forage-type cultivars have been developed specifically for pasture use. It is frequently found as an invader in hay and pasture mixes, as it is very aggressive, particularly on fertile, well-drained soils of the northern states.

Description

Kentucky bluegrass is a long-lived, perennial, sod-forming grass. This cool-season grass has numerous basal leaves and an open, pyramid-shaped panicle attaining heights up to 2 feet. The narrow leaves are characterized by a distinct, boat-shaped tip. The flat or folded leaves have two distinctive grooves the full length of the blade surface. The branches of the panicle are commonly spreading and whorled in groups of three to five. There are three to five florets per spikelet. Florets, when separated from the glume exhibit a silky tuft or web of fine hairs around the base. Flowering is early, taking place in May and June.

The root system is extensive and finely branched. In established stands, the mixture of roots and rhizomes concentrated in the upper 2 inches of soil form an extremely dense, resistant sod. The depth of the root system is variable as to the amount of available soil moisture, but is confined to the upper few inches of soil.

Adaptation

Although it is an Old World introduction, it is widely distributed throughout the United States, except in arid regions. It occurs at all altitudes below alpine regions. Kentucky bluegrass is especially adapted to growth in the cool, humid climate of northern United States. Bluegrass is a sun-loving plant, but does well in semishade during the hot summer months. Although it goes dormant during dry weather, it survives severe drought periods.

Kentucky bluegrass occurs on moist, well-drained soils, in meadows, pastures, fields and open woods. It is neither acid- nor alkali-tolerant, but survives in a pH range of 5.8 to 8.2. It prefers soils of high fertility and medium texture. Large amounts of nitrogen must be available during periods of most active growth, particularly in the spring, early summer and again in the fall.

Limitations

Kentucky bluegrass does relatively well in irrigated and subirrigated situations throughout the growing season. However, under dryland conditions, this grass will go dormant during hot, dry weather, making it relatively unproductive in midsummer. This species is slow to establish, with very little growth and development the first growing season. Once established, it is very aggressive. This species lacks tolerance to extremes in both acidity and salinity. Good productivity is dependent on high fertility levels.

Use for Hay

Kentucky bluegrass is seldom used for hay production. It frequently invades or volunteers in hay mixtures. Since most growth is in the form of basal leaves, it does not generally give heavy yields as a hay crop. This species matures earlier than most species used for hay production.

Use for Pasture

This grass ranks as one of the most palatable pasture grasses. When it is kept actively growing by proper fertilization -- and stays in the vegetative stage -- the protein content remains high throughout the season, varying from 20 percent during spring growth to 10 percent upon maturity. Crude fiber is inversely proportional, with 15 percent in the spring and 25 percent at maturity.

The optimum grazing height is between 2 and 6 inches -- more severe grazing would restrict root and rhizome development, while under utilization would result in weed invasion. In irrigated pasture trials during summer months, cattle gain more weight on Kentucky bluegrass than on orchardgrass or smooth bromegrass.

Seed Production

Seed yields under irrigation are usually 500 pounds per acre or better. Yields of 100 pounds of acre or less can be expected under dryland conditions. No dryland seed production should be attempted in areas receiving less than 16 inches annual precipitation. The cobweb-like hairs at the base of the seed help prevent excessive shatter, but necessitate running seed through a debearder or hammermill to remove these hairs. Seed can be harvested by stripping, direct combining or combining from a windrow. Harvest dates range from mid-May to mid-June. Good seed yield can be maintained up to five years.

* The Montana Interagency Plant Materials Handbook (EB69) is no longer in print, but is available for viewing in
Montana County Extension Service and National Resource Conservation Service Offices.