Kentucky Bluegrass

Kentucky bluegrass (Poa pratensis) receives its name from its blue inflorescence, an open, branching, pyramid-shaped structure known as a panicle. The panicle is 1-1/2 to 5 inches long and 1 to 3 inches wide. The waving branches bear spikelets on their ends. Each spikelet has three to six flowers capable of producing abundant awnless seed.

A bluegrass plant ranges from 18 to 24 inches in height and is characterized by slender, upright stems. The stems are slightly flattened in shape.

The leaves vary in length from 2 to 10 inches and average 1/4 inch in width. The blades are flat or folded and feel soft to the touch. Take a good look at the veins of the leaf for an interesting characteristic of Kentucky bluegrass—along the keel are two oddly transparent veins sometimes compared to racing stripes. The tip of the leaf is considered boat-shaped. Each leaf arises from a sheath with large veins.

Kentucky bluegrass is capable of forming dense mats thanks to its abundant rhizomes, tough stems that grow horizontally under the ground. The rhizomes of bluegrass typically grow two to four inches beneath the surface of the soil, but sometimes deeper.

Distribution

Kentucky bluegrass can be found growing wild across all of Kansas in a variety of sites. It does well in open woods and meadows, as well as sites where the soil has been disturbed, such as tilled fields and overgrazed pastures.

Despite its adaptation to this wide range of locations, bluegrass is actually rather specific in its preferences and will not truly thrive unless its needs are met. The soil must be well drained and medium in texture—Kentucky bluegrass cannot tolerate compacted clay. Its pH preference is 6.0 to 7.0. It will be most productive in areas of full sunlight, although it can stand some shade if it receives adequate moisture and nutrients.

Kentucky bluegrass really excels in climates where the average daily July temperature does not exceed 75 degrees and where the air is humid.

Life Cycle

Photo courtesy of USDA NRCS

This species is a cool-season perennial. It takes off quickly in early spring and grows aggressively while the weather is cool, starting from the previous year’s roots and continuing with a fresh new crop of roots. It also puts out rhizomes with amazing rapidity, and can spread through additional shoots known as tillers.

Kentucky bluegrass flowers from May through July. It often reproduces asexually by forming seeds in the ovary wall of the flower. Most of the seeds, therefore, are clones of the mother plant. Once the flowering process is completed and the summer grows hot and dry, Kentucky bluegrass protects itself from drought damage by going dormant.

It turns green again as days become short and cool. During this second period of growth, the plant focuses on putting out more rhizomes, spreading itself to collect solar energy. Late in the fall, the growth slows down and carbohydrates are stored in the abundance of new rhizomes to provide the nutrients needed to start all over again in the spring.

Ecology

Kentucky bluegrass is not a native of the United States, but rather Europe, northern Asia, and some of the mountainous areas of Algeria and Morocco. It arrived on our shores with settlers during the colonial period, and it spread across the nation with the pioneers.

Since that time, Kentucky bluegrass has made itself a desirable source of food and shelter to many different animals, ranging from insects to grazing mammals. It hosts May, June, and Japanese beetle grubs, while it provides forage to deer, turkey, and rabbits. Its seeds feed many different songbirds and rodents.

Uses

The forage value of Kentucky bluegrass is well known across the nation. It provides excellent nutrition to horses, cattle, and sheep when the weather is cool, although its production is limited when the temperatures rise. It can be seeded as a monoculture, but mixing it with a legume will increase its nutritional value still further and provide for the nitrogen needs of the grass stand, as well. Plant into either a tilled or a no-till seedbed with adequate fertility and an optimal pH value, no deeper than 1/4 inch. Once the stand is established, it can be grazed in the early spring as soon as the grass reaches five inches tall. Always leave a stubble of about two inches to prevent subsequent weed invasion.

The thick mat formed by Kentucky bluegrass is also excellent for erosion control purposes. It can be used to stabilize banks, pond edges, and field borders, and it is a good grass cover in orchards. The type and amount of maintenance bluegrass will require in this role will depend on the specific application. Where the height of the grass is not an issue, it will only need to be mowed once a year to control weeds and keep the stand looking its best.

Even in the hotter, drier climate of Kansas, Kentucky bluegrass has some potential in lawns and recreational areas. It is best adapted to the Glaciated Region, with its higher rainfall and quality soils. However, those in other parts of eastern Kansas who are fortunate enough to have loam soil should be able to grow Kentucky bluegrass, as well. In Kansas, the best time to plant is September, as the soil will be cooling off and the weeds will be less competitive than in the spring. Before planting, ensure that your lawn seed gets off to a good start by tilling in high-quality organic matter such as compost at a rate of three to six cubic yards per 1,000 square feet of lawn. Broadcast seed at a rate of two to three pounds per 1,000 square feet. To ensure seed germination and seedling survival, water the lawn two or three times a day for the first couple of weeks. After this establishment period, Kentucky bluegrass should require irrigation only weekly and only in hot weather. Mow whenever the grass reaches three inches tall to bring it back down to a height of two inches (never lower than this, or the plants will be damaged and become more susceptible to disease). In the fall, the lawn can be core-aerated every year or two to avoid compaction problems.

Hazards

Kentucky bluegrass can be invasive in cool, wet climates. This is unlikely to be a serious problem in any part of Kansas.

The pollen of Kentucky is a major contributor to late-spring allergies.

Similar Species

Fescue Species
The various varieties of fescue used in lawns may present some identification challenges at first glance. However, bluegrass has thinner blades and produces a fine-textured turf. All types of fescue have wider blades, thus producing a coarser turf.