DO I NEED A COOL-SEASON OR A WARM-SEASON GRASS?
, 6 min reading time
There are approximately 10,000 grass species on earth. Of this vast group, there are only about 50 species that can be used as turf. This very special group of grasses have certain characteristics that separate them from the other grasses. Most importantly, they must tolerate continuous defoliation so that we can mow them. Most grasses will die if they are cut back to within a couple of inches of the ground. For instance, corn is a grass. If it is defoliated, it will die. This is true of the vast majority of grasses and they could never be used on your lawn. They also must maintain a highly dense stand at the low mowing heights that we use on turf. There are many grasses that can be defoliated, but they form an open ground cover that would not be suitable for use as a turfgrass. They need to have a fine texture. Many of the large grasses, like corn and bamboo have leaves that are far too wide to ever be used as a turf. Our lawn-grasses have narrow leaves that will form a dense stand when mowed. Finally, they have to have a good, dark-green color to form an attractive stand in the landscape. Again, this is a very special group of about 50 grasses in the entire world.
This limited group of grasses are further divided into cool-season and warm-season species. It is important to get the right type of grass for your location. What works in Minnesota will not likely work well in Florida. And what works in Arizona will unlikely work well in North Dakota. As the names would indicate, cool-season grasses do best in cooler areas. They are best adapted to temperatures in the range of 72 degrees Fahrenheit (F). Warm-season grasses can tolerate high-temperatures in the range of 90 degrees F or more. Cool-season grasses will maintain their color well into the fall in northern regions and throughout the winter in more temperate climates. Whereas, warm-season grasses will go dormant and turn brown once temperatures fall below 50 degrees F. The reason for these differences in tolerance for cold can be found in their photosynthetic systems. The cool-season grasses have what is known as a C3 photosynthetic system and warm-season grasses as C4. The names have to do with the way in which sugars are formed in the photosynthetic process. Cool-season grasses begin with a 3 carbon sugar and warm season grasses begin with a 4 carbon sugar. There are also important differences in their cellular structure. The net effect is that warm-season grasses are much better at tolerating the hot conditions of summer.
Warm-season grasses also have a deeper root system. Most of the roots of a cool-season grass are in the upper 12 inches of soil. The roots of warm-season grass are generally found in the upper 3 feet. This leads to important differences in how we fertilize and water them during the season. With a few exceptions, warm-season grasses will generally tolerate a lower mowing height.
The cool-season grasses include the bluegrasses, the fescues, the ryegrasses and the bentgrasses, along with a few other minor use species, The warm-season grasses include the bermudagrasses, buffalograss, the zoysiagrasses, St. Augustinegrass, bahiagrass, Carpetgrass, as well as a few other less commonly used species.
Kentucky bluegrass is the most commonly used lawn-grass in the northern region. Bermudagrass is the most common in much of the south, although this will vary some with location. In Floridan and the Gulf Coast region, St. Augustinegrass is very widely used as a lawn grass. You will also see Bahiagrass and Carpetgrass in some locations. Zoysiagrass is also widely-used through the central parts of the country like Kansas, Missouri, and Southern Illinois, although its use is more limited in northern and far southern regions.
Again, you need to choose the right grass for your location. In the far north, like Minnesota, North Dakota, or Wisconsin, your choice is going to be easy. You need a cool-season grass. For a lawn, you will likely use Kentucky bluegrass, or Kentucky bluegrass combined with fescues, and/or perennial ryegrass. If you are in Alabama or Arkansas, bermudagrass will likely be the right choice,
Through the midsection of the country, there is a region known as the transition-zone. This is a region where the summers are a little too hot for cool-season grasses and the winters are a little too cool for warm-season grasses. In the transition zone, you will have a choice. In Kansas City, you may find a Kentucky bluegrass lawn or a tall fescue lawn, next to zoysiagrass lawn, next to bermudagrass, and maybe a buffalograss lawn. Each will have its advantages and disadvantages, and in this region you will want to do a little more research before making a choice,
In drier, warmer, temperate regions like Dallas, Texas water availability may be a concern. While cool-season grasses will stay green most of the winter, they require far more water over a year’s time than do warm-season grasses, which will spend most of the winter in a dormant condition. The pretty green color is desirable, but it comes at a cost. In more northern regions like Nebraska and Iowa, some warm-season grasses can be used, but they will be brown from September to June.
So, where can you get accurate information on which grass will be best for your location? In most states, there is an agricultural extension service that can provide specific information. In transition zone states, like Missouri, the answer may be different if you live in the northern part of the state than in the southern portion. Be sure to be very clear about you exact location. Also be ready to provide them with information on your desires and objectives for your turf area. Your seed dealer will also be a good source of information. They will know your area well and they often tailor seed mixtures and blends for a particular region. Beware of local big-box stores. They sells seed, but generally lack trained people to answer your questions.
If you have made a decision on species, but want more refined information on the specific cultivars of that species that is best adapted to your location, there is a web site at ntep.org. NTEP stands for National Turfgrass Evaluation Program. This service is located in Beltsville, MD. Its purpose is to distribute grasses for testing to Agricultural Universities, where they are evaluated each year for regional adaptation. Most major University turfgrass programs are involved in this testing and you should be able to find specific information for your state and surrounding states. Your seed dealer will be familiar with the results of these trials and they use them to develop their packaged seed for specific locations.
Nick Christians, University Professor of Horticulture, Emeritus, Iowa State University
books: http://www.amazon.com/Nick-Edward-Christians/e/B001H6SB7A/ref=ntt_dp_epwbk_0
turf blog: http://www.iaturf.blogspot.com/
Fundamentals of Turfgrass Mgt. 5th ed http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119204631.html
Web site: https://www.hort.iastate.edu/directory/nick-christians/