Turf grasses are labeled as either “warm season” or “cool season.” It confuses people who are not in the industry. You might surmise from their names that these types of grass can’t survive in the opposite seasons. In other words, the assumption would be that warm season grass can’t live in cold climates, and cool can’t live in tropical areas. This is not true. The reality is a bit more complicated.
How are these two classes of turf grass different? Warm season grasses do well in Spring and Summer when temps are 80-95 degrees. Cool season grasses thrive in temps from 60-75 degrees. However, cool and warm season grasses have nothing to do with the time of year that they thrive. The names refer to the regions where temps are optimum for most of the year. Therefore, cool season grasses do well in northern states, and warm season grasses do well in southern climates.
Generally speaking, cool season grass thrives in the Northeast US and the Pacific Northwest. These areas are generally cool and humid. There are some warm season grasses to be found in the Western and Southern parts of this region when temperatures are warmer. Cool season varieties of grass are bluegrass, tall fescue, fine rescue, and rye. The cool arid zone of the Midwest and Western states also allow cool season grasses to prosper so long as irrigation is available. Some types of cool season grass like Canada bluegrass and wheat grass are well suited for colder parts of the area since they can endure arid conditions. Cool season grass doesn’t go dormant, but some “rust” or get buried in snow in fall and winter.
Warm season grass is usually located in southern states and in humid areas of the southwest. Such areas around the Gulf of Mexico are havens for Zoysia, St. Augustine, bahiagrass and centipede grass. In comparison, bermuda grass does well in dryer places. In winter, the cool season varieties are popular in overseeding, because they can produce green lawns year-round. Warm season grass turns brown after the ground temps fall below 65 degrees. During these periods, the warm season grass is dormant. For folks who want a green yard all year long, overseeding with cool season types (like annual rye) is a common practice.
What then is the “transition zone?” There’s a large area of the central and eastern states from parts of North Carolina to Northern Virginia that cuts across the country. These areas are difficult to grow grass in due to it being too cold for warm grasses in winter, and too hot for cool grasses during summer. Many turf pros use a mixture of grasses in this transition zone. Sometimes professionals use Latitude 36 Bermuda and Geo Zoysia, as both grasses tolerate cold weather.