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Kentucky Bluegrass
Poa pratensis

Kentucky bluegrass is the predominant high-quality lawn grass for northern climates. It is a well-adapted, perennial species that spreads by underground lateral stems called rhizomes. This enhances its ability to form sod and recover from traffic damage.

Kentucky bluegrass is most successful in full sun and well-drained, fertile soil. It should be fertilized regularly and mowed to 2.5 inches. Kentucky bluegrass requires irrigation to avoid summer dormancy associated with warm, dry conditions.

The major disease problems associated with Kentucky bluegrass include fungal diseases such as leafspot, dollar spot, and necrotic ringspot. Pest problems include surface and root feeding insects such as white grubs and billbugs.

There are many improved cultivars of Kentucky bluegrass bred for close mowing (less than 1 inch), high traffic areas, disease resistance, and extremely dark green color.

Kentucky bluegrass requires more than two weeks to emerge from seed sown in the soil, and can take up to 8 weeks to produce a dense sod. This limits its use in overseeding and renovation when a mature lawn is needed in a short time.

It also is less competitive with fast germinating weeds and other lawn grasses such as perennial ryegrass during establishment. Studies show that as little as 30% perennial ryegrass mixed with 70% bluegrass will result in 80% perennial ryegrass 3 years after establishment. To establish stands of Kentucky bluegrass, you need to use mixes with less than 20% fast-germinating species.

The downside of Kentucky bluegrass's aggressive, sod-forming rhizomes is that they can contribute to excessive thatch development. (Thatch is the surface accumulation of organic matter composed primarily of dead and decaying stems and roots -- not grass clippings.) Under high fertility and cool, moist soil conditions, thatch may have to be removed physically or core cultivation (aerification) can be used to mix soil particles with the thatch layer.