Our blog posters and customers are wonderful folks, and recently one of these wonderful folks asked me a question about the difference between warm and cool season grasses. Excellent question ! Hope my answer clarifies, rather than confuses the issue ! It’s simpler than you think !
Cool season grasses grow well under cool, moist spring and summer conditions like those found in most of the northern tier of states and southern Canada, east of the Mississippi river. They begin growing as soon as the soil gets to a temperature of 41 degrees F which in the north means basically as soon as the frost comes out of the ground in the spring. In milder areas farther south, these grasses will retain their green colour all winter long and may actually do some growing during winter warm spells. These grasses grow optimally under cool, humid conditions with soil temperatures in the 50’s and 60’s. However, the trade off is that these grasses don’t tend to do well in the heat of summer. In the north, hot, dry weather typically doesn’t last long; after a month or at most two, things cool down and the grass comes back green. Farther south, the weather heats up early and stays hot long into the fall. High soil temperatures and long, hot summers promote rapid evapotranspiration. Under these sorts of conditions, cool season grasses suffer badly. In really hot places like Florida, cool season grasses die out completely as even the winters aren’t consistently cool enough for them to do well.
Warm season grasses don’t start growing until the soil temperature approaches 60 degrees, and they really thrive when the soil temperature is over 80 degrees. In south Florida, these conditions occur for most of the year. As one moves farther north, the length of time which warm season grasses thrive grows shorter and shorter, until eventually they peter out entirely.
The area where both warm and cool season grasses overlap is (appropriately) called the transition zone. The transition zone begins (roughly) at the Ohio River and it extends south a couple of hundred miles into the northernmost sections of SC, GA, AL and MS. As such, our farms are located toward the southern side of the transition zone. What this means in practical terms is that warm season grasses grow and persist here better than do cool season grasses, although both exist in relative abundance. At this latitude, even a few miles can make a considerable difference in species profile. Our new farm is located slightly farther south than our current home place, and it contains a markedly higher proportion of warm season grasses than does our current place. Similarly, the farther up toward and into Kentucky one moves, the more prevalent cool season grasses become.
The middle of October heralds the onset of cool nights in our part of the world which in turn cause our local warm season grasses to begin to go dormant for winter. Because of this, and because our cool season grasses haven’t started to come on yet, our pastures often look their worst in October and early November, despite “optimal” grass growing weather. (Melissa here – February is another month where the pastures look their worst)
Examples of Cool Season Grass Species = Kentucky Bluegrass, Canada Bluegrass, Meadow Brome, and Meadow Foxtail.
Examples of Warm Season Grass Species = Dallisgrass, Common Bermuda, Hybrid Bermuda, Zoysiagrass, Big Bluestem, Little Bluestem.
Hope this explains the difference between the two type of grass adequately !
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