Ornamental · Poaceae
Kentucky Bluegrass
Poa pratensis
Give it full sun and steady water, and Kentucky bluegrass fills in as a dense, self-healing lawn.
Full sun
Every 3–7 days
14–30 days
USDA 3–7
Overview
When someone pictures a classic cool-season lawn, this is usually the grass they've got in mind. It grows into a fine, dense turf in a deep green that leans toward blue, and it spreads all on its own by underground rhizomes that quietly fill in scuffs and bare spots. Funny thing about the name, though, since it actually came over from Europe and northern Asia with early colonists, and it's been the backbone of northern lawns ever since.
So what really sets it apart? That self-repairing habit. While bunch grasses just sit there in clumps, bluegrass creeps sideways and re-knits worn ground, which is exactly why it holds up on yards and playing fields that see real foot traffic. The catch is patience, because it's slow to get going from seed and usually wants a full season or two to thicken up.
It does ask for sun and a bit of cool-weather watering, and that's about it. In a hot, dry summer the lawn browns out and goes dormant, looking done for while the crowns sit alive underground, and then it greens right back up once the rain and cooler nights come around. Give it the light and moisture it's after and it pays you back with one of the toughest, best-looking turfs you can grow up north.
Care
The short version: full sun and a steady 1 to 1.5 inches of water a week, mowed to about 2.5 to 3.5 inches, on fertile well-drained soil, with a feed in spring and fall.
Light
Bluegrass really wants full sun and only stretches to part shade at best. Push it into real shade and it thins out, weakens, and invites powdery mildew, so it's smarter to save the shady ground for a fine fescue.
Water
Give it about 1 to 1.5 inches (2.5 to 4 cm) of water a week while it's growing, and go for a deep soak rather than little daily sips. During a hot, dry spell it'll brown out and go dormant, but don't sweat it, because the crowns hang on and the lawn wakes back up once cool, moist weather returns.
Soil
It's happiest in fertile, well-drained loam sitting around a pH of 6.0 to 7.0. Heavy, soggy ground holds onto disease, so good drainage does you more good than piling on the fertilizer.
Temperature
This is a cool-season grass, comfy anywhere from about -29°F to 75°F (-34°C to 24°C). It shrugs off tough northern winters and greens up early, though it does run out of gas once high summer really heats up.
Humidity
Regular outdoor air suits it just fine, so there's nothing to chase there. What actually matters is air movement, because still, muggy corners let dollar spot and mildew take hold.
Feeding
Feed it a nitrogen-rich lawn fertilizer in spring and again in fall, when it's growing hardest. Skip the heavy nitrogen in summer, though, since all it does is stress dormant turf and feed the disease.
Pruning
Mow to about 2.5 to 3.5 inches (6 to 9 cm), and bump the blade up to 3.5 inches or higher in summer heat to take the edge off. Its strong rhizomes build thatch over time, so plan on a dethatch every now and then.
Repotting
none
Size & spacing
Mowed turf only stands about 2 to 4 inches (6 to 9 cm) tall, while each plant creeps 6 to 18 inches (15 to 46 cm) wide by rhizome. That sideways spread is exactly what lets a stand close ranks into solid sod and patch up its own bare spots.
When to plant
Bluegrass settles in easiest once the heat lets up, so there's no rush to get going. Sow seed or lay sod in late summer to early fall, when the temperatures ease off and the rain comes back, and the new lawn gets rooted before winter. Spring is your backup window, and if you ever let a stand grow tall it'll send up blue-green flower heads in late spring to early summer.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Seed (10 to 14 lb per acre, no deeper than 1/4 in) or lay sod in late summer to early fall when temperatures moderate and rains return; spring seeding is the second-best option.
- Harvest: Grown as mowed turf and normally kept from flowering; if left unmowed it produces blue-green flower heads in late spring to early summer. Establishes as a dense sod over one to two seasons via rhizomes.
Hardiness
USDA hardiness zones: 3–7
Temperature: down to -40°C
Troubleshooting
Most bluegrass headaches show up as browning, thinning, or a bare patch, and more often than not it's the weather or the way the lawn's been mowed and fed. The trick is telling a harmless summer nap apart from disease or grub damage, then stepping in before a thin spot settles in for good. Find what you're seeing below and act while a little help still goes a long way.
Purple-brown blade spots that rot down and thin the lawn
This one's leaf spot and melting-out, a couple of fungi that move in during cool, wet spring weather, and they love turf that's cut short and pushed hard with early nitrogen. It kicks off as dark purplish-brown spots with tan centers on the blades, then works its way down to rot the crowns and roots until you get thin, bare patches. Want to slow it down? Raise the mower, ease up on the spring feeding, and help water and air move through the lawn.
Fix:
- Raise the mowing height to reduce stress on the crowns.
- Avoid heavy quick-release nitrogen in spring.
- Improve drainage and air movement and apply a labeled fungicide if needed.
Dead patches where the turf peels up like a rug
If the sod rolls back to bare soil, something's been eating the roots underneath. Nine times out of ten it's white grubs, the C-shaped larvae of Japanese beetles, chafers, and June beetles, with billbug larvae chewing through stems and crowns as the runner-up. And those skunks, birds, or raccoons tearing up the lawn? They're a dead giveaway, since they're digging for the grubs. Take a peek at the root zone to be sure, then water in a labeled grub product at the right time and keep the lawn well watered so it can shrug off any light damage.
Fix:
- Confirm grub numbers by inspecting the root zone and treat when populations are high.
- Apply a labeled grub-control insecticide at the proper timing and water it in.
- Keep turf well watered to help it outgrow minor damage.
Straw-brown lawn that quits growing in midsummer
Before you assume the worst, know that this is almost always summer dormancy and not a dead lawn. The grass basically clocks out when heat and drought pile up, and the crowns keep ticking along underground the whole time. So what's the move? Either keep it green with 1 to 1.5 inches (2.5 to 4 cm) of water a week, or let it nap and just sprinkle a bit every 2 to 3 weeks until the cooler, wetter days roll back in.
Fix:
- Apply about 1 to 1.5 in of water per week to keep the lawn from going dormant, or let it go dormant and water lightly every 2 to 3 weeks to keep crowns alive.
- Avoid heavy traffic on dormant turf.
- Resume normal care when temperatures cool in fall.
Thin, tired spots wherever the shade lands
Wondering why a few corners never fill in? It's the shade, because this grass really wants full sun and gives up fast without it. You'll see it struggle worst under trees and along the north wall of the house, while the sunny stretches stay nice and thick. A white film called powdery mildew likes to show up in those dim, stuffy spots too. The fix is easy enough: open up the branches overhead to let light through, or just overseed the shade with something tougher like fine fescue.
Fix:
- Prune or thin overhead trees to let in more light.
- Overseed shaded spots with more shade-tolerant grasses such as fine fescues.
- Raise mowing height and reduce nitrogen and irrigation in shade.
Little tan coin-sized spots that grow into each other
Those small silver-dollar spots are dollar spot, a fungus that pops up in warm, muggy weather when the lawn's running short on nitrogen. Get down close and you'll notice light-tan lesions rimmed in reddish brown, and sometimes a soft cobwebby film on dewy mornings. It's not hard to shut down, though. Keep the nitrogen steady and moderate, water early so the blades dry off by lunch, and only reach for a labeled fungicide if it really starts to spread.
Fix:
- Maintain moderate to adequate nitrogen fertility to promote recovery.
- Water deeply in the early morning so foliage dries quickly; remove dew by mowing early.
- Apply a labeled fungicide (alternating modes of action) if damage is severe.
A spongy lawn with a dead mat sitting on top
Here's the catch with such a vigorous spreader: all those busy rhizomes slowly lay down thatch, a brown layer of dead stems wedged between the green blades and the soil. Once it gets past about 1/2 inches (5 cm) thick, the lawn feels spongy underfoot and starts hanging onto disease and drought stress. No big deal to handle, though. Core aerate or power rake in early fall, and go a little lighter on water and nitrogen so that mat stops piling up.
Fix:
- Core aerate and/or dethatch (power rake) in early fall.
- Avoid excessive nitrogen and overwatering that speed thatch buildup.
Toxicity
Good news if you've got animals around: Kentucky bluegrass is not poisonous. It's a non-toxic lawn and forage grass, safe for cats, dogs, and grazing livestock alike, and it doesn't turn up on the ASPCA's toxic-plant lists at all. The only real catch? The pollen from an unmown, flowering lawn, which can kick off hay fever in people and pets who lean that way.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats Safe
No need to worry about the cat, since there's nothing poisonous here for them. If one gulps a big mouthful and brings it right back up, that's just a full stomach talking, not a toxin.
Dogs Safe
The dog can chew it and roll around on it all it wants. The only thing worth watching is the grass pollen, which can leave a sensitive pup itchy and watery-eyed with hay fever.
Horses Safe
Horses graze it happily, and why not, since it's a prized pasture grass that does them no harm at all.
Rabbits Safe
Rabbits can nibble the fresh blades no problem. Just bring any new forage in slowly, because a sudden switch upsets a rabbit's gut even when the plant's totally harmless.
Livestock Safe
Cattle, goats, and sheep all do great on it, which makes sense since it's one of the tastiest forage grasses around.
Birds Safe
Songbirds and backyard poultry can peck at the seed and tender shoots without any trouble.
People Safe
It's totally fine to handle and walk on. If you're prone to hay fever you might sneeze near the airborne pollen once an unmown lawn flowers, but that's just an allergy, not poisoning.
The grass itself is not poisonous. Grass pollen can trigger hay-fever allergies in sensitive people, and dogs or cats that nibble large amounts of grass may occasionally vomit, but this is not a sign of poisoning.
Varieties
Most lawns go with improved turf-type cultivars instead of wild bluegrass. These are the names worth keeping in your back pocket when you shop for seed or sod.
'Midnight'
It's a favorite improved turf type, loved for its really dark blue-green color and a low, tight, compact habit that takes close mowing in stride.
Kentucky bluegrass blends
These are mixes of a few improved cultivars, often teamed up with fast perennial ryegrass, that spread the disease-resistance bets around and hurry along a lawn that would otherwise be slow to fill in.
Hybrid (Texas × Kentucky) bluegrasses
They're crosses with Texas bluegrass that keep their color and keep right on growing through summer heat and drought way better than pure Kentucky bluegrass does.
How to propagate
There are two easy ways to start a bluegrass lawn: from seed, which is cheap but slow, or from sod and plugs that fill in fast and then spread on their own.
SeedModerate
Late summer to early fall (or spring) · Germinates in about 14 to 30 days and forms a full sod over one to two seasons
Sow in late summer or early fall, or fall back to spring, scattering about 10 to 14 pounds per acre and keeping the seed no deeper than 1/4 inch. Here's the thing, it likes to take its time, sprouting over 14 to 30 days and needing one or two full seasons to knit into a dense sod, so a lot of folks mix in faster perennial ryegrass to hold the ground while the bluegrass catches up.
DivisionEasy
Spring or early fall · A few weeks once roots and rhizomes re-knit
Lay sod pieces or plugs in spring or early fall and they'll take hold in just a few weeks. After that? The grass pretty much handles it for you, sending out underground rhizomes that creep into bare ground and give the lawn its handy self-repairing habit.
Myths
Kentucky bluegrass is blue and comes from Kentucky.
The blades run green to blue-green and never actually blue, and the name just comes from the blue-green flower heads an unmown lawn throws up in early summer. And it isn't even American, believe it or not. It came over from Europe, northern Asia, and the mountains of North Africa with European colonists, so it's neither blue nor a Kentucky original.