Climate Zones of the U.S.
Basic knowledge of climate zones can be very useful. Grasses will always thrive best when planted in the correct zone.
In the U.S. there are four primary grass adaptation zones. There is also an additional region located in the central U.S. called the Transition Zone. These zones should not be confused with the USDA's Eleven Plant Hardiness Zones used for trees and other plants. The plant hardiness zones are described farther down this page.
The turfgrass zones in the U.S. are oddly shaped because they follow along temperature and humidity contour lines. While almost all grasses will grow in any zone for at least part of the year, all grasses are best suited for a specific climate zone. Unlike container plants, you can’t bring your grass indoors when conditions no longer favor it, so choosing a good grass for your area is important.
Location Of Climate Zones
The climatic zones in the U.S. are labeled as Cool/Humid, Warm/Humid, Cool/Arid, Warm/Arid. The transition zone was added because of overlapping temperature and humidity conditions in the central U.S. It stretches from the extreme eastern edge of New Mexico to the central East Coast. The northern edge reaches into central Illinois and as far south as northern Louisiana. The center of the transition Zone is considered by many to be the most challenging place in the U.S. for quality turf. The following chart shows the location of the different turf climate zones.
With the changes in climate in the U.S., with longer winters and more rain in areas, you may need to be more careful with some borderline plants. Choose some that are solidly in the center of your climate zone.
Grass Adaptation Zone Map courtesy of Dr. Nick Christians, Dept. of Horticulture, Iowa State University.
Preferred Grasses In Each Climate Zone
- The Cool/Humid zone in the Northwest can receive a great deal of moisture. This can be problematic for some grass types. The fescues, bluegrass, ryegrass, are common lawn grasses in that area. In fact, the State of Oregon is known for growing the highest quality turf-type fescues and seed production. Although the mild temperatures of the northeast favor cool season grasses, zoysiagrass and buffalograss can be found in the eastern reaches of the zone where conditions are much drier.
- The Cool/Humid section is in the northern half of the Mid-West and extends throughout the Northeast. Cool season grasses dominate in this area. Warm season grasses are not favored as much in this area because the summers are too short and the winters are too long and cold.
- In the Warm/Arid zone, Buffalograss and bermudagrass are commonly used grass types. This section stretches through the Southwest as far as central Texas. However, many homeowners in Southern California seem to favor tall fescue lawns even though summers can be quite long and hot. Sprinkler systems are necessary because temperatures can rise above 110 degrees for many days at a time. However, it is an example of tall fescue's ability to survive in heat that would kill other cool season grasses.
- The Cool/Arid zone located in the west is best adapted for cool season grasses as long as it is irrigated. Buffalograss is increasingly being used in many areas because of its drought hardiness.
- The Warm/Humid climate zone in the south is best adapted for warm season grasses. Bermudagrass is very common in this area. Along the coastal regions, St. Augustinegrass seems to be preferred because of turf quality and good shade tolerance. Carpetgrass, Zoysiagrass, and Centipedegrass are also used within this region. Cool season grasses are not used very often except when overseeding bermudagrass in winter.
- The area known as the Transition Zone is so
named because of the transition between cool season grasses and warm
season grasses. There is no one grass type that best fits this area. Its
winter temperatures can be too cold for some warm season grasses and
too hot in the summer for some cool season grasses. The exceptions are
perennial ryegrass and zoysiagrass. Both species are extremely well
adapted here. However, tall fescue is probably the most popular cool
season grass with bermudagrass and zoysiagrass being the most popular
warm season grasses.
I observed in southern Missouri that the majority of lawns were cool season grasses. When I crossed over the border into Arkansas, there was a sharp increase in warm season grasses, especially bermudagrass. The Missouri/Arkansas line is roughly in the center of the transition zone and the central dividing line between warm and cool season grasses.
Some cool season grass cultivars were bred to be able to grow in places where warm season grasses dominate, if that is what you prefer. You will have to check to see if they can survive in your zone and what water requirements they have, especially in drier locations.
In Conclusion...
In every climate zone, grass will respond to light and temperature changes. Each grass species will emerge from winter dormancy as soil temperatures rise in spring. Cool season grasses will thrive best in temperatures of 65 to 75 degrees. Growth will slow as temperatures rise. Warm season grasses are better adapted for temperatures between 80 and 95 degrees and will go dormant as soil temperatures approach 50 degrees.
There are some exceptions, one being perennial rye. It is a cool season grass, but has poor cold tolerance and can be injured in the in cold winters. It is best used for overseeding warm season grasses or as a lawn grass in the transition zone.
One more thing that can help in choosing the right grass, is by checking out your local university extension office. They can help you with any specific questions you may have for your area. You can also look at the National Turfgrass Evaluation Program. The program tests the different grass types in different locations around the country to see how well they perform. Many of the nation's universities that have agricultural and turfgrass programs are the sites for these tests.
The USDA Plant Hardiness Zones
The climate zones for plant hardiness focuses primarily on the minimum cold temperatures starting in the north and moving south. Trees and other are assigned a climate zone based on their ability to withstand specific drop in temperature before injury. In the U.S. there are eleven zones. Keep in mind that these zones do not consider high temperatures, which can vary greatly.
Click on the link to see an interactive map of the USDA Plant Hardiness Zones
Click here to access the National Turfgrass Evaluation Program Website
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