The question of when grass starts growing has a complex answer that depends entirely on location and the specific type of grass. Grass growth is not determined by the calendar; instead, its cycle depends on environmental cues, especially temperature changes after winter dormancy. Understanding these factors helps determine when the growing season begins in a specific region and how to prepare the lawn for spring. The timing dictates when essential maintenance activities must be performed for a healthy, vibrant lawn.
The True Trigger: Soil Temperature
The moment grass wakes up from its winter rest is determined by the sustained temperature of the soil, not the air temperature, which fluctuates wildly in early spring. Air temperature often rises faster than ground temperature, which does not reflect conditions at the root level. Grass roots are insulated by the soil and require consistent warmth to begin absorbing nutrients and moisture.
The critical measurement is taken at a depth of two to four inches below the surface, where the majority of the roots reside. When this soil layer maintains a specific temperature for several days, it signals to the grass that the environment is stable enough to support new growth. This difference between air and soil temperature explains why attempts to fertilize or seed based on the calendar often fail, as the roots are not yet biologically active. The required sustained soil temperature varies significantly between the two main types of lawn grasses.
Timing for Cool-Season Grasses
Cool-season grasses, such as Kentucky Bluegrass, Tall Fescue, and Perennial Ryegrass, are commonly found across the northern United States, the upper Midwest, and the Pacific Northwest. These grasses thrive in cooler conditions, and their growing season begins relatively early. Root growth can begin when sustained soil temperatures reach the 40°F to 50°F range, which often occurs from late February to early April, depending on latitude.
Initial activity focuses primarily on root repair and carbohydrate storage, not rapid blade growth. The most vigorous growth, including visible greening and the need for frequent mowing, happens when soil temperatures are consistently between 50°F and 65°F. This period is their peak season before summer heat forces them into a semi-dormant state. Therefore, in many northern areas, the grass starts to emerge from dormancy in late winter or very early spring.
Timing for Warm-Season Grasses
Warm-season grasses, including Bermuda, Zoysia, and St. Augustine grass, dominate the Southern and Gulf Coast regions. These varieties enter a complete dormancy during the winter, turning brown and ceasing all visible growth. They require much higher, sustained warmth to “green up” and resume their active growth phase.
These grasses need the soil temperature at the four-inch depth to remain consistently between 60°F and 70°F before they fully emerge from dormancy. This usually places their activation period later in the spring, often from late April through May. In cooler parts of the transition zone, it may be early June before these varieties begin their robust growth cycle. This slow start is a defense mechanism, as attempting to grow too early risks damage from late-season cold snaps.
First Actions After Growth Begins
Once the first signs of green growth are visible, the timing for certain lawn care activities becomes important for the season’s success. The initial action should be a slow, gradual first mowing, set at the highest height possible to remove dead, brown leaf tips and encourage denser growth. Waiting for the soil to dry out and firm up is important before running equipment over the lawn to prevent compaction.
The most time-sensitive task is applying pre-emergent herbicide, a chemical barrier that prevents weed seeds like crabgrass from germinating. This must be applied before the soil temperature consistently reaches 55°F, the point at which many undesirable weed seeds begin to sprout. Applying it too late makes the product ineffective because the weeds will have already emerged. A soil test is also beneficial at this time, providing an accurate measure of nutrient levels and pH balance before any fertilizers are applied.