Kentucky bluegrass is one of the most recognizable lawn grasses in the U.S. It is used in the cool-season and transition zones and is most often mixed with another cool-season grass. If you want a top-notch Kentucky bluegrass (KBG) lawn, you’ll have to put in the work, though. To look its best, KBG requires a moderate to heavy fertilizer program, weed control, and irrigation, not to mention disease control. If you’re interested in this high-maintenance grass, we’ll reveal the pros and cons of this cool-season beauty.
Kentucky bluegrass at a glance
Classification: Cool-season grass
Spreads by: Rhizomes
Shade tolerance: Low to moderate — prefers full sun
Drought resistance: Moderate, but will survive by going dormant
Foot traffic tolerance: Low to moderate, but recuperates well
Maintenance needs: Moderate mowing frequency; a high-maintenance grass
Mowing height: 2-3 inches
Potential for disease: Moderate to high
Soil pH: 6-7
Soil type: Good drainage, fertile
Other notes: Produces a dense lawn under ideal conditions; many of these traits (shade tolerance, drought resistance, etc.) vary widely by cultivar, with newer cultivars generally being hardier, more resistant to disease, etc.; mow taller in summer; most often mixed with other species, such as tall fescue, in home lawns
What is Kentucky bluegrass?
KBG is a rhizomatous cool-season grass that is prized for its good looks and ability to recover from traffic wear. This popular grass prefers full sun (light shade is tolerable) and likes deep, fertile soils in which to grow. Kentucky bluegrass is used in the transition zone and further north in cool-season lawns. Pure KBG lawns are rare due to their fussy nature. A mix with other cool-season grasses is usually preferred in home lawns to strengthen against summer heat, disease, shade, and generally make it a lower-maintenance grass.
Pros and cons of Kentucky bluegrass
Kentucky bluegrass may seem like the dream lawn, but it’s not for everyone. Check out these pros and cons to help you learn more about Zoysia’s strengths and weaknesses.
✓ Gives a cleaner cut than grasses with tougher blades like tall fescue
✓ Better cold tolerance than perennial ryegrass or tall fescue
✓ Good disease tolerance when managed well
✓ Goes dormant during droughts — not likely to die
✓ Cultivar growing requirements vary widely, so you can choose the one that best suits your lawn (dozens of cultivars to choose from)
✓ Aggressive rhizomes help the turf to recover from wear and tear
✓ Seed or sod
✗ High water requirement
✗ Root system is shallow
✗ Low shade tolerance
✗ Not a high-traffic grass
✗ Prone to thatch, disease, and insects
How to establish Kentucky bluegrass
Seed KBG in the fall as you would any cool-season grass. KBG is slow to germinate (two to three weeks), so you’ll need to hand-weed if weeds start to pop up.
If you put down sod, almost any time of year will work, but stay away from summer. Cool-season turf is already stressed during the heat of summer, and a new root system will struggle.
How much does Kentucky bluegrass cost?
Kentucky bluegrass sod: Costs between 30 and 55 cents per square foot
Kentucky bluegrass seed: A 3-pound bag of KBG seed starts at around $20
Caring for Kentucky bluegrass
Since KBG has shallow roots, mowing tall is important. The taller you mow, the deeper roots you’ll have since shoot height is proportional to rooting depth. Take off no more than ⅓ of the grass blade per mow (called the ⅓ Rule of Mowing), and leave the mulched clippings on the lawn for a free fertilizer treatment at each mow. Mow from 2-3 inches for the best results.
In hot summer weather, you can either let KBG turn a nice shade of brown and go dormant or you can water, sometimes more than 1 inch per week, and keep it green.
No matter which season of the year, water in the early morning hours, before 10 a.m. at the latest, and only water when the grass tells you it needs water (changes color, footprints stay on the lawn). This is known as deep but infrequent watering, which helps the grass to go deep in search of water and strengthens the root system.
Just as you can decide whether to let the lawn go dormant, you can decide how much you want to fertilize your KBG lawn. It will look better with more frequent nitrogen applications, but if “looks” aren’t your main concern, you can dial back how much you fertilize during the year. Keep in mind, though, that KBG loves nitrogen, so don’t think you can eliminate this step completely.
Late summer into fall is the best time to apply most of your fertilizer. Apply from 1-5 pounds of fertilizer per 1,000 square feet per year, depending on the level of maintenance you desire and the look you want. Use two to four of your total yearly nitrogen applications in the fall. Late summer and fall applications help the grass recover from summer stresses, strengthen the turf for winter, increase shoot density, and bolster its color.
You can apply in spring as well, but wait until after the lawn is fully green and growing to apply nitrogen (slow-release, preferably). Nitrogen applied too early will push the grass too hard as it comes out of dormancy and deplete carbohydrate reserves. This will weaken the grass and make it more susceptible to drought stress, insects, and disease.
Dethatching and aeration
Excessive thatch is a common problem in KBG lawns, especially ones that are highly fertilized. Thatch becomes problematic when too many stems, roots, and other organic materials lay undigested between the grass and the soil surface. Some thatch is beneficial, but too much keeps water and air from reaching the roots and encourages disease and insects.
Generally, ½ inch of thatch or greater is going to start to cause problems, so you want to dethatch at that point. After you remove the thatch, bag the debris and compost it. You don’t want to leave it on the lawn.
Core aeration machines remove some thatch as they pull plugs of soil from the lawn. If you have compacted soil and thatch, both dethatching and aeration may be required. Whichever you choose, plan to dethatch and/or aerate only in fall or spring.
Note: If you have a lawn that is a mix of KBG and tall fescue, thatch may not be an issue at all.
Disease, insects, and weeds
Disease: Kentucky bluegrass can be susceptible to many diseases, but disease tolerances vary widely by cultivar. Here are a few that are common:
A few tips to prevent disease and fungus in your KBG lawn: Allow proper air circulation, minimize excessive thatch, aerate compacted soils, and give the grass as much sun as possible. These basic cultural practices go a long way to make disease less of an issue in your KBG lawn. A few more tips: Water deeply but infrequently, mow at the proper height, and fertilize as your soil test recommends.
Another strategy is to plant KBG in a mix (with tall fescue or other cool-season grasses). The different grasses introduce different strengths to your lawn, so if one disease hits, some grasses will be less affected and your whole stand of grass won’t get a TKO.
Early detection is key, and that, combined with cultural practices, is a good starting point to reduce harmful insects in your lawn. Check out your state’s Extension bulletins to see which insects are most prevalent in your area so you can be on the lookout or take preventive action.
The good news for weed haters is that the cultural practices that help reduce disease, insects, and increase tolerances to droughts and other stresses also reduce weeds in the lawn. For example, some weeds love compacted soils. The solution? Aerate annually, if needed, to reduce compaction and reduce the weeds that thrive in that condition. (Caveat: Aeration can bring weed seeds up from the soil. If you wish, put down a pre-emergent after you aerate the lawn.)
A few other examples: Thin spots allow light to penetrate to the soil level and encourage weeds to germinate (crabgrass in particular). Overseed in fall to keep your stand of grass thick. Also, high mowing helps shade the soil and discourages these weeds from germinating. Frequent mowing will prevent seed-bearing weeds from setting flowers and seeds and dropping a new generation of weeds in your lawn.
If you want to put down chemical or natural products, a good strategy is to use pre-emergents in spring to prevent summer annual weeds, in fall to prevent winter annuals, and spot-treat in summer.
Some information taken from Fundamentals of Turfgrass Management, 5th ed. by Christians, Patton, and Law
If you think a Kentucky bluegrass lawn may be right up your alley, contact one of our local lawn care professionals. They can help you select, install, and care for your grass so you can spend your free time doing what matters most.