Kentucky Bluegrass: Mowing Height, Seed Rate and Lawn Care

Mow Kentucky bluegrass at 2.5 to 3.5 inches, dropping toward 2.5 inches in cool spring weather and raising it to 3.5 inches once summer heat arrives. Taller grass has deeper roots and shades out crabgrass seedlings. Never remove more than a third of the blade in one cut, which means mowing before a 3 inch lawn reaches 4.5 inches. In the spring flush that can mean every four or five days.

A mower with a mulching deck returns clippings, which supply part of bluegrass's high nitrogen demand. The EGO POWER+ LM2135SP 21 in. Select Cut Self-Propelled Mower Kit ranges from 1 to 4 inches and the Honda HRX-BE 21 in. Battery Self-Propelled Mower from 0.75 to 4 inches, so both cover the full bluegrass range. See the mowing height chart for mixed lawns.

At 2 to 3 pounds per 1,000 square feet, a 5,000 square foot lawn from bare soil takes 10 to 15 pounds of seed, and overseeding takes 5 to 7.5 pounds. A full acre at the 2.5 pound midpoint needs about 109 pounds. Seeding heavier does not speed things up; crowded bluegrass seedlings compete and thin out.

Labels can be lighter than extension rates. The Jonathan Green Blue Panther Kentucky Bluegrass Seed, 25 lb is labeled for 20,000 square feet new from a 25 pound bag, about 1.25 pounds per 1,000 square feet, and its label germination is 21 to 28 days. For a lawn with partial shade, a blend such as the Pennington Smart Seed Sun and Shade Mix North, 20 lb mixes bluegrass with grasses that tolerate 4 to 6 hours of sun. Because bluegrass is slow, seed only in late summer to early fall; spring seedlings rarely mature before summer heat.

To keep bluegrass green through summer, plan on about 1 to 1.5 inches of water a week from rain and irrigation combined, delivered in one or two deep early-morning waterings instead of a daily sprinkle. Shallow daily watering grows shallow roots and invites disease. If you prefer not to water, let the lawn go dormant and stay dormant; extension services warn that repeated greening and browning drains the plant more than steady dormancy. A light watering every few weeks during a long drought helps crowns survive.

A smart controller like the Rachio 3 Smart Sprinkler Controller, 8 Zone or the Orbit B-hyve Smart Indoor/Outdoor Sprinkler Controller, 12 Zone adjusts run times to weather. Compare them in Rachio vs Orbit B-hyve, or see the best smart sprinkler controllers.

Often, yes. Bluegrass rhizomes and stems build thatch, the spongy layer of undecomposed stems and roots between the soil and the green blades. Up to about half an inch is harmless; beyond that, water and fertilizer sit in the thatch instead of reaching roots. Push a finger or a trowel into the turf to measure. Dethatch when the grass is actively growing, in late summer to early fall or mid spring, never in summer heat.

A power rake such as the Greenworks 40V 15 in 2-in-1 Dethatcher and Scarifier Kit or the corded Sun Joe AJ805E 15 in Electric Dethatcher and Scarifier lifts thatch across a 15 inch path. Core aeration also breaks down thatch more gradually. The trade-offs are in dethatcher vs aerator.

Bluegrass is the hungriest cool-season grass at 3 to 4 pounds of nitrogen per 1,000 square feet per year. Split it into three or four feedings of up to 1 pound each: late summer, early fall and late fall, plus a light late-spring feeding. With a 29-0-3 product like the Jonathan Green Green-Up Lawn Food 29-0-3, 15,000 sq ft, 1 pound of nitrogen takes about 3.4 pounds of product per 1,000 square feet. Spread in two perpendicular passes with a broadcast spreader such as the Scotts Turf Builder EdgeGuard DLX Broadcast Spreader, whose edge shield keeps granules out of beds and off pavement.