Cool season grasses and warm season grasses grow very differently depending on the season. Learn how to tell what grass type you have and what grass type is best for your area.
If you’re new to lawn care, one of the first things you have to do is answer a simple question: Do you have cool season grass, or warm season grass? This is important, because although there are plenty of maintenance tips and practices that apply to both grass types, there are also some pretty distinct differences. In fact, depending on the time of year, cool season grass might have needs that are completely opposite of warm season grass, and vice versa.
Cool Season Grass
Cool Season Grass thrives when air temperatures are averaging between 50 and 80 degrees. In the northern half of the United States, this temperature range usually occurs in the spring, and then again at the end of the summer/early fall as the heat of the summer passes and temperatures begin to cool. That is why cool season grasses have two periods during the year where they are the strongest: Spring, and Fall (as shown in above picture).
In the summer, air temperatures can get above this range for long periods, driving soil temps with it. This is when your cool season grass can struggle, and even go into a period of summer dormancy. Once late summer/early fall hits, your stressed summer lawn begins to green up again and will have another growth spirt until temperatures are consistently below 50 degrees. At this point grass growth will stop and your lawn will enter winter dormancy. As the winter drags on you’ll probably notice your green lawn turn brown or light tan as the whole lawn goes dormant.
Warm Season Grass
Unlike Cool Season Grass, Warm Season Grass likes the heat. It thrives when air temperatures are averaging between 80 and 95 degrees. Since the southern half of the united states has a much longer period of time where they experience this hot temperature range, it makes warm season grass the best choice. There are some downsides however; Most southern states get cool enough during the winter to make their warm season grass go dormant and brown. This period of dormancy can trickle into early spring and start back up again in mid to late fall when air temperatures are consistently below 80 degrees. The only exception is to those in the very south, or south west where temperatures are warm enough in the winter to prevent a dormancy period.
Looking at the chart above you can see that unlike cool season grass which has two periods of the year (spring and fall) where grass thrives, warm season grass has one pro longed period which ranges from late spring to early fall, where grass thrives.
The Transition Zone
The Transition Zone is the area in the United States where you’ll see both cool season and warm season grasses. Sometimes you’ll see neighborhoods where some people have cool season grass while others have warm season grass. You might even see houses with cool season grass in the front and warm season grass in the back (more on that in a second). The reason for these inconsistencies is because it can be tough to make a decision on growing warm season or cool season grass in the transition zone. The challenge is that in these areas, they can have very hot summers, which is great for warm season grass, however they also have cool falls, and winters which more resemble the climate in which cool season grass thrives. If you have warm season grass, this would mean you’d be looking at brown, dormant grass for much of the winter. But, if you were to plant cool season grass the lawn would struggle and most likely die since the summers are too harsh. To keep the grass alive you would need a lot of water and maintenance to nurse it through the summer.
Knowing what to do can be really challenging in the transition zone. Check out some strategies and things to consider when in the transition zone.
Transition Zone Strategies
1. Consider exact location– If you’re struggling to choose between planting warm season grass or cool season grass in the transition zone than take a moment to consider your exact location. Looking at the map at the top of the page, ask yourself if you are in the upper portion or bottom portion of the transition zone. If you’re in the upper portion, than you should probably favor cool season grass. If you’re in the bottom, choose warm season grass.
Also, consider your micro climate. Are you near a body of water where it’s more humid or are you in more of a desert where there is very little rainfall. Even elevation and topography should be considered. A higher elevation can nudge you in the direction of cool season grass. Micro climates are interesting. I live at the base of a mountain and whenever there’s a large snowstorm it seems to stall right at the base of the mountain. There have been storms where I’ve received about a foot more snow than people a couple of miles down the road.
Also, think about your property. Is it in direct sun or is there shade? What is the size of the turf area? Can you irrigate it? If it’s direct sun than cool season grass will be very hard to keep alive during the heat of the summer in the transition zone. However if there’s some shade, and the turf area is small, and you can install irrigation than cool season grass can work.
Also, take note of the kind of grass your neighbors and near by neighborhoods have. You might see a strong trend in your neighborhood and that might make the decision easier. Overall, consider everything when making this choice.
2. Plant cool season grass in the front yard and warm season grass in the back. If your front and backyard are separated by a fence or some other barrier than one thing you can do is plant cool season grass in the front yard and warm season grass in the backyard. You will need to irrigate your front lawn often during the summer but at least it’s only half the lawn. This will leave you with a green lawn all year in the front yard. The warm season grass in the backyard will go dormant during the winter but at least in the front you can still maintain a nice curb appeal. I know a lot of people in the south that use this strategy. It’s a great compromise.
3. Overseed with ryegrass in the fall. Another solution to the problems of the transition zone is to stick with warm season grass throughout the year, but in the fall, once your warm season lawn starts preparing for dormancy you scalp the lawn (mow it really short), and overseed with rye, which is a cool season grass. Essentially, you’re converting your lawn to be a cool season lawn temporarily. This way you’ll have green grass during the winter months. In the spring when temperatures rise and while your warm season grass is still dormant, you begin to cut your lawn really short (scalping it). When your warm season grass comes out of dormancy it’ll start to outcompete the cool season ryegrass and transition back to a dominantly warm season lawn. The ryegrass will be choked out as temps continue to increase. There’s a great write up on how to do this here: Overseed Warm Season Lawn with Ryegrass
4. Minimize turf where possible. Break up large areas of turf by creating landscape beds. This will help you if you have warm season grass or cool season grass. For warm season grass, landscape beds and plantings will help draw the eye away from brown, dormant grass in the middle of winter. If you have cool season grass it will reduce the turf area to a more manageable size. Irrigating a small area all summer is doable so you might be able to have a nice blend of some grass with some plantings.
Best Grass Types for Transition Zone
Northern portions of the transition zone are primarily made up of cool season grasses. Common cool season grasses in this region are Turf Type Tall Fescue (TTTF), Fine Fescue, and Kentucky Bluegrass. With cool season grasses it’s typical to see a mix of several different seed varieties within a lawn. Most cool season grasses mix well together and blend nicely. This is a nice benefit since you can apply a cool season mix and let nature dictate which variety will be the dominant one. Warm season grasses generally don’t mix well so you’re more likely to see a warm season lawn made up of one seed variety only.
How to Identify Cool Season vs Warm Season Grass
If you just moved into a house in the transition zone and you’re not sure if you have cool season grass or warm season grass you’ll have to play detective a little bit to see what you have:
1. Study the spreading habit– Warm season grasses spread via stolons or rhizomes, or both. If you dig out a small section of grass, study the roots. Do they spread out long and horizonal either above the ground (stolons) or below the ground (rhizomes). This is typical of a warm season grass. If you see above ground runners (stolons) then you can be pretty sure you’re dealing with warm season grass.
Cool season grasses on the other hand don’t tend to be strong spreaders. Most varieties form in several clumps that ultimately blend together. The only common exception to this is Kentucky Bluegrass which does have underground rhizomes. Check out more on stolons and rhizomes here: Warm Season Grass Spreading Habit
2. Observe when your lawn is dormant, or struggling. If your transition zone lawn tends to favor the heat of the summer but turns brown during the winter you probably have warm season grass. If it really struggles during the summer but looks better with the cooler weather than you most likely have cool season grass.
3. Take a close look at the blade color, vernation, tip shape, and blade width and compare it to the picture and information chart you can find here: Grass Identification Chart
4. Check with your local county extension. These are great places that help with identifying a variety of plant species, grass types, insects, etc. You can find your local County Extension by using the search here: County Extension by Zip Code
Cool Season Grass Tolerances
Warm Season Grass Tolerances
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