Cool-season turf, often referred to as winter grass, includes species like Kentucky Bluegrass, Fescue, and Ryegrass that thrive in cooler climates. When summer heat and drought arrive, this grass typically does not die but enters dormancy, a state of self-preservation. This physiological pause conserves internal energy and water resources until favorable growing conditions return in the fall.
The Temperature Thresholds of Cool-Season Grass
Cool-season grasses are biologically optimized for moderate temperatures, with their most active leaf and shoot growth occurring when air temperatures are between 60°F and 75°F. Root growth is strongest in even cooler soil, ideally between 50°F and 65°F. When air temperatures consistently rise above 80°F, the grass enters a period of physiological stress.
The stress threshold begins when the grass’s energy consumption starts to exceed its production. Above 75°F, the rate of photosynthesis, which creates energy, declines rapidly while the rate of respiration, which consumes energy, increases. This imbalance leads to an energy deficit that forces the plant to use its stored carbohydrates.
High temperatures severely impact the root system, which is sensitive to heat. Root growth is heavily stunted when the top inch of soil reaches about 75°F, and root death can begin as soil temperatures climb higher. These shallow roots struggle to take up water and nutrients, compounding the heat stress and triggering dormancy.
Distinguishing Dormancy from Death
Determining whether a brown lawn is dormant or dead is important. Dormancy is a natural, reversible state, visually characterized by a uniform, straw-brown color across the entire lawn. The individual grass crowns, the small growing points at the soil surface, remain firm and often show a hint of pale green, indicating life is preserved.
In contrast, dead grass tends to appear in irregular, distinct brown or gray patches, which often suggests a localized issue like disease, pests, or a hydrophobic dry spot. A simple tug test can differentiate the two: dormant grass will resist being pulled from the soil, while dead grass blades will come out easily because the roots and crown have failed.
Most established cool-season lawns can survive in a drought-induced dormant state for approximately three to four weeks without permanent damage. If extreme heat and drought conditions persist beyond this period, especially with daytime temperatures consistently in the 90s, the risk of permanent turf loss increases significantly. The brown blades themselves will not turn green again, but the living crown will send up new shoots when cooler, wetter conditions return.
Summer Survival Strategies for Turf
Management practices during the summer can significantly influence how well cool-season grass endures heat stress. Watering should be deep and infrequent, aiming to deliver about one to one-and-a-half inches of water per week, including rainfall. This practice encourages roots to grow deeper into the soil, making the turf more resilient to drought, while frequent, shallow watering promotes weak, surface-level roots.
Mowing height is another factor in summer survival. Raising the cutting height to three inches or more helps the grass blades shade the soil surface, which keeps the root zone cooler and reduces water evaporation. Never remove more than one-third of the total blade height at any single mowing to avoid stressing the plant.
Fertilization should be avoided during peak summer heat, especially with high-nitrogen products, as this encourages excessive top-growth that requires more water and energy. This added demand puts an unnecessary burden on an already stressed root system. If fertilization is necessary, using a slow-release nitrogen formula is the safer option to provide a steady supply of nutrients without forcing rapid growth.
Distinguishing Dormancy from Death
Determining whether a brown lawn is dormant or dead is a common concern for homeowners facing summer heat. Dormancy is a natural, reversible state, visually characterized by a uniform, straw-brown color across the entire lawn. The individual grass crowns, the small growing points at the soil surface, remain firm and often show a hint of pale green, indicating life is preserved.
In contrast, dead grass tends to appear in irregular, distinct brown or gray patches, which often suggests a localized issue like disease, pests, or a hydrophobic dry spot. A simple tug test can differentiate the two: dormant grass will resist being pulled from the soil, while dead grass blades will come out easily because the roots and crown have failed.
Most established cool-season lawns can survive in a drought-induced dormant state for approximately three to four weeks without permanent damage. If extreme heat and drought conditions persist beyond this period, especially with daytime temperatures consistently in the 90s, the risk of permanent turf loss increases significantly. The brown blades themselves will not turn green again, but the living crown will send up new shoots when cooler, wetter conditions return.
Summer Survival Strategies for Turf
Management practices during the summer can significantly influence how well cool-season grass endures heat stress. Watering should be deep and infrequent, aiming to deliver about one to one-and-a-half inches of water per week, including rainfall. This practice encourages roots to grow deeper into the soil, making the turf more resilient to drought, while frequent, shallow watering promotes weak, surface-level roots.
Mowing height is another crucial factor in summer survival. Raising the cutting height to three inches or more helps the grass blades shade the soil surface, which keeps the root zone cooler and reduces water evaporation. Never remove more than one-third of the total blade height at any single mowing to avoid stressing the plant.
Fertilization should be avoided during peak summer heat, especially with high-nitrogen products, as this encourages excessive top-growth that requires more water and energy. This added demand puts an unnecessary burden on an already stressed root system. If fertilization is necessary, using a slow-release nitrogen formula is the safer option to provide a steady supply of nutrients without forcing rapid growth.