Cool-Season vs. Warm-Season Grass: How to Tell Them Apart and Where Each Grows

Cool-season grasses (Kentucky bluegrass, tall fescue, perennial ryegrass and the fine fescues) grow best when daytime highs run 60–75°F, so they peak in spring and fall. Warm-season grasses (Bermuda grass, zoysia, St. Augustine and centipede) grow best at 80–95°F, peak in summer and turn tan once repeated frosts arrive. The quickest way to tell yours apart is to look at the lawn in midwinter, then check whether it spreads by surface runners.

Below: three identification checks, where each type grows, and the prime growing weeks 24 US cities get, from NOAA’s 1991–2020 normals.

Cool-season and warm-season grass at a glance

The split is biological: cool-season grasses use C3 photosynthesis and warm-season grasses C4. That is why cool-season grasses handle frost and low light better, while warm-season grasses need more heat and light but less water, Illinois Extension explains.⁶ (For how much each needs, see our guide to how much to water a lawn.)

Sources: Virginia Tech,² University of Tennessee,⁴ NC State,⁵ K-State³ and UF/IFAS.¹¹

How to tell which grass you have

Mowing removes the flower heads botanists rely on, so you identify a lawn from its leaves and the way it spreads:

The seedhead, the main identifying feature, is not present in mowed turf.

Three checks, from easiest to most precise:

1. Look at the lawn in winter

A warm-season lawn goes tan after repeated frosts and stays tan until spring: about 4 to 5 months in a typical Virginia winter, says Virginia Tech. The dormant grass is not dead and still protects the soil.² A cool-season lawn keeps more color, and Illinois Extension suggests using that timing as your first clue.⁶

Two things can fool this test. Where frost is rare, as in Miami or Phoenix, winter color tells you little. And a lawn that is green in January but wiry at the soil line may be dormant Bermuda overseeded with ryegrass for winter color.⁷

2. Find a runner, or a clump

Grasses spread in one of three ways. Bunch-type grasses grow in clumps; rhizomes are stems that run below the soil; stolons are runners on the surface that root at their nodes.³ Tall fescue and ryegrass are bunch-type, Kentucky bluegrass has rhizomes, and Bermuda grass and zoysia have both rhizomes and stolons.³ A lawn knitted together by runners on the soil is almost certainly warm-season.

To tell the creepers apart, Virginia Tech notes that centipede shoots alternate along very large stolons, while St. Augustine’s even larger stolons put out shoots side by side, and its blades are the widest, with a blunt tip. Zoysia’s new shoots branch at right angles into a very dense turf.²

3. Check the leaf up close

Pull a few shoots and look where the blade meets the stem. K-State’s identification card (MF2031) checks whether the newest leaf is folded or rolled, the ligule (a membrane, a fringe of hairs, or nothing), the claw-like auricles and the blade.³

Cool-season lawns are usually seeded as blends or mixtures,² so one handful may hold several of these. Still unsure? K-State suggests asking your local extension office.³

Where each type grows: North, South and the transition zone

Cool-season grasses dominate the North and the Pacific Northwest, warm-season grasses the South. In between lies the transition zone, cold enough in winter to challenge warm-season grass and hot enough in summer to challenge cool-season grass, says Texas A&M AgriLife Extension:

the transition zone is the most challenging region in which to grow grass

Extension services in North Carolina,⁵ Virginia,² South Carolina⁸ and Arkansas⁹ place their states in it, and New Mexico State adds northern New Mexico and Oklahoma.¹⁰

Inside the zone, local conditions decide. Virginia Tech’s turf team admits the difficulty:

In Virginia, we can grow eight different turfgrasses, not very well!

Its guide favors cool-season grasses and zoysia in the mountains, adds cold-tolerant Bermuda and centipede in the southern Piedmont, and keeps St. Augustine to the southernmost coastal counties.² In northern New Mexico, elevation largely decides.¹⁰ Florida is firmly warm-season: UF/IFAS says northern grasses grow there only from fall to early spring and do not survive the hot, humid summers.¹¹

No boundary is official. One commercial guide lists parts of 24 states from California to New Jersey; another sends readers to the USDA Plant Hardiness Zone Map, which is built on the average annual extreme minimum winter temperature¹² and ignores summer heat. We found no USDA map of turfgrass zones.

Prime growing weeks in 24 cities

Both grass groups are defined by daytime highs, so weather data can show how each fares in a city. We took the normal daily high at the nearest NOAA station (1991–2020 normals)¹ and counted the weeks it sits at 60–75°F (cool-season prime) and at 80–95°F (warm-season prime), plus the frost season, from the median first fall frost to the median last spring frost.

What the numbers show:

• Seattle never reaches the warm-season range: its normal July high is about 77°F.
• In Minneapolis and Boston, warm-season grass gets only 6–7 prime weeks, and the frost season lasts 4.8 to 6.2 months.
• In Houston and Jacksonville, the 60–75°F weeks fall in winter, from about November to March, while warm-season grass gets 26–27 prime weeks.
• In the cities extension services place in the transition zone, both ranges get 13–24 weeks and the frost season runs 3.9 to 6.5 months: a real season, and a real stress, for both types.
• Phoenix and Dallas spend 19 and 8 weeks above 95°F, past the best range of either group.

Do the numbers match extension observations?

Blacksburg’s longer frost season fits Virginia Tech’s advice for the mountains.² The Farmington row uses daily average temperature, the measure NMSU reported.¹⁰

What these numbers cannot tell you

They cannot draw the edge of the transition zone. Chicago, Columbus, Philadelphia and St. Louis look much like the transition-zone cities: 11 cool-season weeks, 11–17 warm-season weeks and 4.4–5.9 months of frost, against 13, 17 and 4.9 in Richmond. What keeps warm-season grass out of the North is winter injury, which depends on how cold it gets and how long and how wet the soil stays frozen (University of Tennessee).⁴ Monthly normals miss that, along with shade and unusual years. So we do not label any ZIP code cool-season, warm-season or transition zone; follow your state extension service and read the table as context.

What your grass type changes in the lawn calendar

Most lawn jobs are timed to when the grass grows hardest, so the two calendars are nearly opposite.

Sources: University of Tennessee,⁴ Illinois Extension,¹³ Clemson’s Bermuda grass calendar¹⁴ and Clemson’s aeration fact sheet.¹⁵ For dates in your area, see our guides to when to overseed a lawn, when to fertilize, when to apply winterizer, when to aerate, when to apply pre-emergent, when to stop mowing and when to dormant seed.

Related guideWhen to Fertilize Your Lawn: A Schedule by Grass Type and Climate

Your next step

Run the three checks, then look up your frost dates by ZIP code: on a warm-season lawn, the first fall frosts start the browning. More seasonal jobs are in our lawn care guides; the methodology page explains how we use NOAA normals.