Grass growth, which makes a lawn appear lush and necessitates frequent mowing, is driven by cell division and expansion. New cells are produced at the base of the leaf blade and expand to increase the blade’s length. The speed and timing of this activity are not constant, depending entirely on the specific type of grass and the environmental conditions it experiences. Understanding when your lawn is most active requires first identifying the biological category your turfgrass belongs to.
Understanding Cool-Season Versus Warm-Season Grasses
Turfgrasses are categorized into two groups based on their ideal temperature ranges for growth. Cool-season grasses, such as Kentucky Bluegrass and Tall Fescue, are dominant in the northern United States. They are adapted to withstand cold winters, maintain their color through winter, and thrive in milder temperatures.
Warm-season grasses, including Bermudagrass, Zoysiagrass, and St. Augustinegrass, are common in the South and warmer climates. These species are highly tolerant of intense summer heat and often require less water. They enter dormancy, turning brown, once temperatures drop below approximately 65°F.
The “Transition Zone” of the central U.S. presents a challenge, as it is too hot for cool-season grasses in the summer and too cold for warm-season grasses in the winter. Homeowners in this region often select a grass type that can tolerate these extremes or manage a mixture of both.
Optimal Conditions for Peak Vertical Growth
Maximum vertical growth, which visibly lengthens the grass blades, occurs when air temperatures fall within a specific range for each grass type. For cool-season grasses, peak vertical activity happens when air temperatures are consistently between 60°F and 75°F. This results in two distinct periods of rapid growth: late spring into early summer and again in the early fall.
During the peak spring period, cool-season turf emerges from winter dormancy and quickly utilizes stored energy for blade growth. As summer air temperatures rise above 80°F, growth significantly slows, and the grass may enter a semi-dormant state to conserve moisture. Once temperatures drop back into the optimal range in the fall, a second surge of growth occurs as the grass actively recovers and stores energy before winter.
Warm-season grasses require higher temperatures, reaching peak vertical growth when air temperatures are consistently between 80°F and 95°F. Their most vigorous growth period is a single, prolonged event spanning the mid-summer months. During this time, they require frequent mowing to manage the rapid expansion of leaf tissue. Growth slows dramatically once nighttime temperatures fall below 60°F, prompting their transition into winter dormancy.
The Difference Between Vertical Growth and Root Development
Grass growth includes the development of the root system below the soil surface, not just the vertical height that requires mowing. A significant difference exists between the timing of shoot growth and root growth, which is largely regulated by soil temperature. For cool-season grasses, maximum root development occurs when soil temperatures are between 50°F and 65°F, which is slightly cooler than their peak vertical growth range.
Cool-season grasses prioritize root development in the early spring and, more importantly, in the late fall, after intense vertical growth has subsided. The grass shifts energy and resources to thicken and deepen its root mass during these periods, which is crucial for nutrient uptake and drought resistance. Frequent mowing during vertical growth can encourage this subterranean activity as the plant compensates for the lost leaf area.
Periods of stress, such as intense heat or cold, cause the grass to enter dormancy, halting visible growth entirely to conserve energy. For warm-season grasses, the root system is active alongside vertical growth during the hot summer. They also use late summer and early fall to store carbohydrates in their roots and rhizomes for winter survival. Supporting this deep root structure with proper watering and late-season fertilization is beneficial for the long-term health of the lawn.