Exploring the Differences Between Cool-Season and Warm-Season Grasses

You may not realize that not all grass is the same. There are cool-season grasses and warm-season grasses. It is important to learn the difference between these types of grass, even if you leave your lawn care to a lawn service.

Knowing more about the type of grass you have will enable you to provide better care for your lawn and supervise any work done by professionals. Read on to discover the answer to the question, “What is the difference between cool-season grasses and warm-season grasses?”

Differences Between Cool-Season and Warm-Season Grasses

The Major Difference: Active Growth Timing

The main difference between cool-season vs. warm-season grass is seen when the plant is in its active growing phase.

Warm-season grass will have its active growth during the late spring. It then goes dormant in early or mid-fall. It is rightfully named warm-season grass because of the fact that it starts to “green up” when evenings start getting warm in late spring.

By contrast, cool-season grass “greens up” or is in active growth earlier. This phase begins in mid-spring. The grass’ active growth period also lasts longer, going until late fall when the plant becomes dormant. Importantly, cool-season grasses require regular summer watering, and without it, they go dormant in the summer heat.

Some of the most common cool-season grasses include Kentucky bluegrass, tall fescue, fine fescue, and perennial ryegrass. Common warm-season grasses include carpet grass, bahiagrass, St. Augustine grass, Bermuda grass, centipede grass, and zoysia grass.

The Science Behind the Difference in Grasses

If you are curious about why cool- and warm-season grasses exist, it’s because they rely on slightly different types of photosynthesis. Photosynthesis involves capturing carbon dioxide (along with water), which the plants convert into oxygen and sugar.

C3 photosynthesis has three carbon atoms in the first molecule made during photosynthesis. C4 photosynthesis has four carbon atoms in this molecule. Those molecular differences make certain plants thrive in different sets of growing conditions.

Cool-season grass goes through C3 photosynthesis, while warm-season grass goes through C4 photosynthesis.

Sunlight and Shade Requirements

Warm-season grasses tend to prefer sunlight and do poorly in the shade. By contrast, cool-season grasses are more tolerant of both shade and sun. They need about a half-day or three-quarters of a day of full sun.

How to Choose Which Type of Grass to Plant

Most people who compare cool-season vs. warm-season grass do so while deciding which type to use for their lawn. You can keep these factors in mind when deciding.

If You Prioritize a Green Lawn

If your goal is to keep your lawn green for as long as possible, you may want to consider cool-season grass—this is because cool-season grasses are generally more tolerant of varying conditions and hold up better in cooler weather.

If You Prioritize Minimizing Water Use

If your goal is to choose a grass that requires as little water as possible, you should consider warm-season grass. Remember that you will have to use more water to maintain the health of your cool-season grass, especially in the summer. That said, some cool-season grasses are known to be more water thirsty than others, such as Kentucky bluegrass.

If You Are at a High Elevation or Further North

Cool-season grasses tend to do much better than warm-season grasses at higher altitudes. That’s why LawnMart typically recommends cool-season grasses to its Greater Toronto area clients.

By contrast, homeowners in the southern United States, for instance, would do better choosing warm-season grasses. With the warmer climate in the area, cool-season grasses would require an even greater deal of water to maintain active growth.

It’s worth noting that there is also a transition zone in the United States, where choosing between the two types of grass gets more complicated. Those living in this area will always want to consult experts. Luckily for those in the Greater Toronto area, using cool-season grasses is the more obvious choice.

When in Doubt, Ask the Experts

Of course, if you aren’t sure whether to plant cool or warm-season grass, you should ask lawn care professionals who can help you choose the appropriate type of grass based on your expectations and preferences.

Planting Tips for Cool-Season Grasses

The differences between warm and cool-season grasses should always be considered when you look at the ideal planting conditions.

Most cool-season grass is grown from its seed and will germinate well if the evenings are cool. You can start sowing the seeds in mid-spring, even before the last usual frost date. You can still sow the seeds until early summer.

That said, you should not sow cool-season grass seeds when the temperatures reach 90 degrees or higher. At this temperature, it is simply too hard to give the young seedlings enough moisture to germinate.

Bluegrass “Bella” is an exception to the rule, as you typically plant it as plugs. You will have to do this about six to eight weeks before your first frost or early to mid-fall.

Planting Tips for Warm-Season Grasses

You should wait to plant warm-season grass seeds or plugs until after the final average frost date for your area. The seeds need the consistently warmer night temperatures of this time of year.

When you water them enough, these warm-season plugs will establish roots quickly.

Make sure you don’t plant warm-season grass too early, as the colder nights can delay active growth and keep the grass dormant. This can even give weeds an opportunity to grow.

If you are waiting to plant warm-season grass until the end of the warmer weather, do so at least eight weeks before your area’s first average frost date.

How Do You Know What Type of Grass You Have?

You can make an educated guess about whether you have warm or cool-season grass based on where you live. You can also ask a lawn care company to determine it for you.

Look at the Spreading Roots

Warm-season grass will typically spread out, either above the ground (as stolons) or below it (as rhizomes). Ground runners or stolons always indicate warm-season grass.

If there is not much spreading, then you likely have cool-season grass. Just keep in mind that Kentucky bluegrass, a common cool-season grass, does feature underground rhizomes.

See When Your Lawn Struggles

Another good method to determine the type of grass on your lawn is to check when your grass does poorly. If it tends to do poorly in the heat of the summer, you likely have cool-season grass. If it does fine in the peak of summer but struggles when the weather gets cooler, you likely have warm-season grass.

Get Professional Assistance with Grass Care

You don’t need to struggle to take care of your lawn, whether you have cool-season or warm-season grass. You can leave it up to professionals. Experts like those at LawnMart can suggest the ideal grass based on the local climate and your property’s needs.

If your grass is already established, professionals can quickly identify whether it is warm-season grass or cool-season grass. From there, they can make recommendations for proper care and maintenance. If you want to expand your lawn by planting even more grass, you can consult these professionals about the best type of grass to use and hire them to do everything for you, from planting to maintenance, so your lawn stays healthy throughout the year.

LawnMart can easily handle a variety of grass types in a range of environments. Call us to find out how we can help transform your lawn. Get a free quote today!

Michael Schäfer

President – LawnMart Inc.

Years of Experience: 31 Years

  • Land Class 1 and 3 Licenses Since 1993
  • Pest Control Operator License Since 1995
  • PIC Accredited Pest Technician Examiner Since 2004
  • Biting Flies Control License Since 2020

Michael Schäfer is President and Founder of LawnMart Inc. After training privately under Dr. Larry Whiddell of Ohio State University, he became a Lawn Technician at Barefoot Grass Lawn Services (1993) and leveled up to Tree/Shrub Care Manager before taking over all Canadian operations as Area Manager. In 1996, Michael founded LawnMart Inc., which has since grown into a multi-award-winning company that cares for thousands of lawns in the Golden Horseshoe area.