Grasses are classified as either warm-season or cool-season types based on how they grow. Understanding the difference between the two types will help you choose the best one for your yard and help you properly take care of your turf.
Warm-season grasses
Warm-season grass varieties are typically grown in the South, where daytime summer temperatures are hot, and winters are mild, often without any snow. These grasses green up in late spring when nighttime temps warm up and brown in late September to October.
They have the following characteristics:
- Air temperatures must reach 60 to 65°F, and soil temps have to hit 50°F for growth to begin in the spring.
- Most of their biomass is produced during the hottest part of the year, from July to September, when average temperatures are 85°F to 95°F.
- At higher temperatures, they increase their rate of photosynthesis rate to utilize nitrogen and phosphorus better.
- They are more adapted to abiotic stressors such as drought and high temperatures than their cool-season counterparts.
- These grasses prefer full sun and are very intolerant of shade.
- In areas with cold winter temperatures, the grass goes dormant, and the blades turn brown until the spring.
- Warm-season grasses are planted via grass plugs when nighttime temps are warm. They do best when planted in late spring or summer.
Common warm-season grasses include Bahiagrass (Paspalum notatum), Bermuda grass (Cynodon dactylon), Buffalo grass (Buchloe dactyloides), carpetgrass (Axonopus affinis), centipedegrass (Eremochloa ophiuroides), St. Augustine grass (Stenotaphrum secundatum), and Zoysia grass (Zoysia japonica).
Cool-season grasses
Cool-season grasses are grown in the Northern areas of the United States, where summertime temperatures are milder, but winters may be harsh with a fair amount of snow. This type is greener for a longer time than warm-season grasses. They green up in early to mid-spring and stay green until October or November.
They have the following characteristics:
- Active growth doesn’t start until air temperatures are above 40 to 42°F.
- Most biomass is produced in the spring and late fall when air and soil temperatures are cooler, between 65 and 75°F.
- They tolerate some shade but need at least half a day of full sun, if not more.
- To maintain their lush color in the hot summer, they require more water to stay green. They go dormant without regular watering.
Cool-season grasses are typically grown from seed and are best sown in spring or fall. They germinate well when nights are cool.
Common cool-season grasses include annual ryegrass (Lolium multiflorum), creeping bentgrass (Agrostis palustris), creeping red fescue (Festuca rubra var. rubra), Kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne), and tall fescue (Festuca arundinacea).
What Are The Best Transition Zone Grass Types
A transition zone is characterized as a region where both hot summers and cold winters are experienced. In the United States, a transition zone is found in the horizontal band across the middle of the continent. The mixed climate of these zones presents growing challenges because it does not neatly fit warm or cool system grasses into its ecosystem.
Choosing a cool season grass will provide a longer green period but upkeep will be much higher to prevent dormancy due to heat in the high summer months.
The alternative, warm season grasses, are heartier in the summer months, requiring less attention, but will go brown as the weather turns cooler.
Due to changes in climate (warming in the summer and more mild winters) has seen a shift towards warmer conditions. When coupled with improvements in more cold resistant grasses, in many cases a warm season grass is preferable to cold season in a transition zone.
Improvements in Yukon Bermuda Grass and Riviera Bermuda Grass have made them perennial in most transition zone climates. Even with their improved cold tolerances, improved varieties of Bermuda Grass still run the risk of winter dormancy turning a brown color.
Despite this, Bermuda grass has been found to be a very aggressive grass with fast growth and good shade tolerance. The heartiness of the improved Bermuda grass varieties has made it an ideal choice for those growing in transition zones.
Browning and dormancy of warm seasons grasses can be overcome through two methods.
The first and most effective is the overseeding of a warm season grass with a cool season grass. This allows for continued growth during the cooler months achieves a year-round green lawn.
Care must be taken to ensure compatibility between the two grass types, the prime warm season types are Bermuda Grasses and Zoysia Grass.
The second, less desirable option is to plant a grass that maintains a pleasing color during dormancy. Typically this would be a Zoysia Grass that turns a golden color when dormant. The benefit of this route is simplification of only on grass type needing to be cared for verses many.
When choosing a transition zone grass, typically the best course of action is to determine what others in the region have had good luck with. Northern transition grasses will have different requirements than southern regions. Increasingly warm season grasses are becoming the dominant choice as improvements are made in various varieties that can be found commercially.
Can You Mix Warm and Cool Season Grasses In A Lawn?
Grasses used in lawns come in two types, warm and cool season. Due to their different growing characteristics the choice between warm and cool season grass can be difficult, especially if choosing for a yard that is located in a transition zone (a region with both hot summers and cold winters).
In the north, where summers are mild and winters are cold, cool season grasses are the dominant choice. These grasses have a heartier grow cycle that allows most growth to occur in the early to mid-spring before temperatures rise too high.
Best growth for cool season grasses occurs when the temperature is between 65 and 80°F.
In the fall months, cool season grasses will remain green for much longer than their warm season counterparts. The main weakness of cool season grasses is that they are not very drought tolerant and they will go dormant in summer months if not sufficiently watered.
When seeding a lawn, different cool season grass types can be mixed to ensure even growth throughout. Common types of cool season grasses are Kentucky Bluegrass, perennial ryegrass and fine fescue.
Just as cool season grasses are predominant in the north, warm season grasses are dominant in the south. These grasses require much less water than cool season varieties and cope well with extreme heat.
Warm season grasses grow best when the temperature is between 80 and 95°F. The trade-off is that they take longer to green up and will go dormant much fast once the weather turns and outside temperatures drop.
Unlike cool season grasses, warm season grass types vary widely and are not conducive to mixing with other types. This is in part due to different grow rates, color, texture and water requirements.
The most commonly found types of warm season grasses are Bermudagrass, St Augustine Grass and Zoysiagrass.
Due to their widely different characteristics, warm and cool season grasses should not usually be mixed.
Different grow habits, colors and textures will result in a lawn that is both mottled and patchy. When used in a pasture mixing of different types of grass will result in a longer forage but is not ideal for residential use. The only exception to this rule when Bermudagrass is overseeded with perennial ryegrass for winter coverage.
Care must be taken however that the two types of grasses do not over compete. This combination, when used correctly, provides a year round green.
