Kentucky bluegrass is the most popular cool-season grass, loved for its beautiful emerald and blue-green colour and its soft texture. It’s also the most needy of grasses, requiring a lot of fertilizer, a lot of care for insects and disease, and a lot of water. Is Kentucky bluegrass right for you? Keep reading to find out.
What Is Kentucky Bluegrass (Poa pratensis)?
Zone 3 – 9 (USDA)
|Single-species blend, multi-species mixture
|Full sun, poor shade tolerance
|5.8 – 7.0
|Yearly nitrogen (lb/1,000sq ft)
|4 – 5 (high)
|Mow to 2 – 4 inches
|Excellent tolerance of cold, low tolerance to heat, salt, insect, and disease
|14 – 30 days
Whether or not you know it, when you think of the ideal lawn, you’re probably imagining Kentucky bluegrass. It’s one of the most widespread grasses in cool-season climates. It has a fine, soft emerald or blue-green foliage. As it’s rhizomatous, it can self-repair, filling in any gaps, and becoming a thick carpet that can withstand high foot traffic.
However, it comes with high costs and high maintenance. Kentucky bluegrass has shallow roots that make it unable to hold on to essentials like nutrients and water. Bluegrass has pretty low resistance to insects and disease. It’s one of the least sustainable grasses, as many homeowners rely on synthetic fertilizers, herbicides (weed killers), and pesticides, as well as additional irrigation, to keep this grass healthy.
However, you don’t have to give up your dream of a bluegrass lawn if you can find the right cultivar. Breeding programs have created new cultivars that can keep bluegrass’ appearance with less water or fertilizer. Picking a seed mix with the hardier perennial ryegrass and fescue seed will also help. Contact your local University Extension office to find out which cultivars they recommend for your area.
You can also apply organic lawn care techniques, like using organic amendments and hand weeding, to lower your environmental impact while keeping your lawn looking nice.
Pros and Cons of Kentucky Bluegrass
|High maintenance, as they require a lot of water, fertilizer, and pest, weed, and insect management.
|Establishes easily from seed once germinated
|Low tolerance to heat, shade, salt, insects, and disease
|Long germination period
How To Grow Kentucky Bluegrass
Like other cool-season grasses, the best time to sow bluegrass is during the fall, during its peak growing season. It germinates best between soil temperatures of 50F to 65F, or air temperatures of 60F to 75F. Sow at least 6 weeks before the first frost date of the year. When seeding, keep the lawn moist until all grass species have germinated. Once seeds germinate, Kentucky bluegrass will establish quickly.
Kentucky bluegrass tolerates being mowed as short as 2 to 2.5 inches, although it still benefits from being kept longer (3 inches in spring and fall, 4 inches in summer). In the spring, you can start mowing as soon as the grass grows again.
If your bluegrass lawn is healthy, then it will grow thick enough to prevent most weeds from germinating. When weeds do sneak through, hand pull weeds. This manual effort is still the most effective method for many weeds.
Bluegrass requires more nitrogen than grasses like perennial ryegrass and fescues, but you can still use natural methods. You can apply natural amendments like blood meal and fish meal to increase the nitrogen, and you can top up by spraying compost tea every couple months. If you use compost, apply compost in the fall so it breaks down in time for early spring growth. You can top up compost in the spring with a smaller amount.
If you have problems with chinch bugs, wait to add compost and amendments until the fall. Chinch bugs prefer spring-fertilized lawns.
Bluegrass requires at least 1 inch of water per week (whether from irrigation or rain) in the spring and fall, while in the summer it needs at least 2 inches or more to keep from going dormant. If your lawn goes dormant, water it only a couple inches per month, and it’ll bounce back when temperatures cool. In the fall, gradually reduce the watering to every two weeks.
If you have clay or loam soil, water deeply less frequently (4 inches every 14 days, for example). Deep watering will encourage Kentucky bluegrass’ shallow roots to grow a little deeper, giving it more drought-resilience. If you have sandy soil, you’ll need to water shallowly more frequently (1 inch every 7 days) as sandy soil doesn’t keep water very well.
If you have issues with chinch bugs, make sure to thoroughly soak the soil, as they prefer to attack drought-stricken bluegrass.
Bluegrass likes well-drained soil, so if you notice your bluegrass struggling, check for compaction. Core aerate before overseeding to relieve compaction. When seeding, you can either core aerate or rototill.
Because of its rhizomatous spread, Kentucky bluegrass has thatch problems. If thatch builds up more than a 1/2 inch, then you’ll need to dethatch. For light cases of thatch (under 1 inch), you can remove a short enough thatch with a rake. If you’re core aerating for overseeding, then a core aerator will actually remove enough thatch to skip this step. If the thatch is thick and matted, you may need to rent a dethatcher. Keep between 1/4 to 1/2 inch of thatch, as it’ll shade the soil and keep it moist for longer to help solve one of Kentucky bluegrass’ major drawbacks.
Do not use a dethatcher if you don’t need to, as the process is really hard on the grass. The grass will need time to recover and it’ll be more vulnerable to pests and disease.
Frequently Asked Questions
Where does Kentucky bluegrass grow best?
Kentucky bluegrass is a cool-season grass for climates with mild summers and cold winters. It prefers a well-draining clay-loam soil that is slightly acidic. It also requires a lot of water and full sun, so it grows best in places with abundant rainfall and sunny days.
How long does it take to grow Kentucky bluegrass?
Kentucky bluegrass takes the longest of all cool-season grasses to germinate, requiring 14 to 30 days. But once it germinates, it establishes itself quickly. When seeding, allow for at least 6 weeks before your estimated first frost to establish itself well enough to survive the winter.
How can I make Kentucky bluegrass germinate faster?
You can encourage Kentucky bluegrass to germinate faster by creating ideal germination conditions. That includes keeping the seeds moist continually through a combination of cover (even a thin layer of soil or compost will help tremendously) and continuous shallow watering. The light cover will absorb moisture and keep seeds moist longer than just leaving them on top of the soil.
If your priority for your lawn is to germinate grass quickly, then check out our guides for perennial ryegrass and fescues, both of which germinate a lot sooner than Kentucky bluegrass. Choosing a mix with one or both of these other grasses will also help your bluegrass grow as the early sprouts will help hold moisture to the remaining seeds. Still keep the soil moist until the Kentucky bluegrass germinates.
Will Kentucky bluegrass choke out weeds?
Healthy Kentucky bluegrass lawns grow thick enough to prevent most weeds from germinating. All plants need open, moist soil and sunlight to germinate, and Kentucky bluegrass’ thick rhizomatous growing habit prevents access to these two essentials. Weeds are more of a problem when starting a new lawn from scratch, taking advantage of bluegrass’ long germination period, and where the grass has thinned because of damage. Overseeding bare spots will help prevent weeds.
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.