Will Tall Fescue Choke Out Warm Season Grasses?

Growth Considerations

• If both fescue and warm-season grasses exist in a lawn, the soil conditions and weather regime dictate which grass type prospers. Like other cool-season grasses, fescue develops deep color and lush growth when the soil is moist and air temperatures cool, in the range of 40 to 80 degrees Fahrenheit. By contrast, warm-season lawns stop growing and go dormant when the soil becomes cool and daily high temperatures no longer get above 70 degrees F.

Competition

• Fescue grass can choke out warm-season grasses when the growing conditions favor more rapid growth of fescue. The gray area exists during the transitional period of spring and fall, when the weather temperature trend favors one over the other. If both grass types are green and growing when temperatures hover around 70 to 80 degrees F, fescue may choke out the warm-season grass or vice versa. The deciding factor as to which grass wins in the competition depends on soil moisture or the height the lawn is mowed. Cutting any lawn grass too low can weaken and stress it, causing it to yellow and retard its growth. For example, cutting fescue lower than 2-inches tall stunts it and can give an advantage to a low-growing warm-season grass such as Bermuda or centipede grass, which is mowed to 1- to 1 1/2-inches tall.

Species Insight

• If the lawn's fescue grasses are vigorous and the warm-season grass density or vitality is low, fescue can begin to choke out competition if the weather trend is for further cool, moist conditions. If summer temperatures get hot enough or summer drought is common in your region, the fescue can choke out the warm-season grasses until conditions kill back the fescue. The result is bare spots where the fescue died and a limited carpet of warm-season grass needed to fill-in. If temperatures remain hot, the warm-season grass will prosper if soil is warm and moist, and the fescue will remain dormant or die. Bermuda grass lawns tolerate seasonal overseeding of fescue better than centipede, zoysia or St. Augustine grasses, according to Bob Polomski of Clemson Cooperative Extension.

Other Insight

• Tall fescue will survive longer if in shadier areas of a warm-season lawn as temperatures heat up in summer. Therefore, fescue will likely choke out or merely grow better under the shade trees in the yard. Aerating lawns stresses plants, so it is done only at the beginning of the grass' best growing season. For example, aerating fescue lawn in spring as temperatures heat up and its growth wanes stresses it and can kill it. In this case, the warm-season grass isn't likely choked out. Conversely, aerating the same lawn in fall weakens the warm-season grasses, but benefits the fescue.