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Aug 162012

Kentucky bluegrass (Poa pratensis) is the most widely adapted and most commonly used lawn grass in the United States. It does well in sunny areas throughout Idaho, is very cold tolerant, and will form a dense, high quality turf when grown in full sunlight. The leaves have a characteristic boat-shaped leaf tip and a prominent midrib.

Kentucky Bluegrass

A. Boat-shaped leaf tip of Kentucky bluegrass. B. Midrib on top of leaf surface. (Photo Courtesy: A.J. Turgeon, Penn State University)

Kentucky bluegrass has a spreading growth habit with aggressive rhizomes allowing it to form a dense sod and fill in bare spots quickly during establishment. These rhizomes also make it challenging for gardeners striving to keep this grass from creeping into adjacent flower beds. Additionally, this aggressive, spreading growth habit makes Kentucky bluegrass susceptible to thatch development especially under high fertility and moist conditions. Yearly aerification and prudent fertilization and irrigation practices will help keep thatch to a manageable level.

A major limiting factor of Kentucky bluegrass on home lawns is its lack of shade tolerance. Under heavy tree shade or on the north sides of houses that receive substantial shade during the day, it will thin and develop powdery mildew, a white, powdery fungus on the leaves. Raising the mowing height in shady areas will help some, by giving it more leaf area to catch light.

Kentucky bluegrass requires medium to high inputs of water and fertilizer depending on the desired quality level of the lawn. For most home lawns, Kentucky bluegrass should be maintained at a mowing height of 2 to 3 ½ inches. Mow towards the higher end of the range to develop a deep root system. Kentucky bluegrass requires 2 to 5 lbs of nitrogen (N) per 1000 ft2 per season. Irrigation requirements will range from 1 to 1 ½ inches per week in the spring to 1 ½ to 1 ¾ inches per week in the summer. Kentucky bluegrass will tolerate extended periods of drought by going dormant as long as it is allowed to properly harden prior to the drought.

Establishment from seed can be quite slow, requiring 10 to 20 days for germination. Using a straw mulch or planting a seed mixture with a small percentage of perennial ryegrass, which germinates much faster, will provide some protection for the slower germinating Kentucky bluegrass seeds. Laying sod will bypass this germination problem, but proper care during sod grow-in is just as important as proper care during seed establishment. Kentucky bluegrass sod is readily available in Idaho from garden centers and directly from sod producers.

There are many varieties of Kentucky bluegrass available giving a wide range of disease resistance, wear tolerance and green color. Most of the grass seed available at your local garden center or lawn and garden areas of major chain stores will have varieties of superior quality. Be sure to check the label of the seed package to ensure you are buying ‘named’ varieties and not ‘variety-not-stated’. Named varieties listed on the label indicate that the variety(ies) is an improved variety and has gone through several years of testing. It is best to choose a blend of three or more Kentucky bluegrass varieties to ensure a broad resistance base to diseases.

This fact sheet from Colorado State University outlines the positive and negative characteristics of Kentucky bluegrass as well as provides some management considerations.

 August 16, 2012