St. Augustine grass (Stenotaphrum secundatum) is a popular warm-season turfgrass known for its dense, carpet-like growth in the southern United States. During cooler months, this grass enters dormancy, turning straw-brown as growth slows significantly. The grass is not dead but conserves energy until conditions become favorable for active growth. Understanding the precise triggers that initiate the transition back to a vibrant green lawn is crucial for proper spring maintenance.
Environmental Conditions That End Dormancy
The primary signal that cues St. Augustine grass to break dormancy and begin its active growth phase is the sustained warming of the soil. While rising air temperatures are noticeable, the temperature of the root zone is the actual mechanism controlling the spring transition. This turfgrass requires a consistent soil temperature, typically measured at a four-inch depth, to be in the range of \(60^\circ\text{F}\) to \(65^\circ\text{F}\) for several consecutive days.
Once this thermal threshold is met, the rhizomes and stolons can initiate new shoot growth and the characteristic green-up begins. If the soil temperature dips back down after a brief warm spell, the grass may temporarily stall or even partially reverse its transition. Increasing day length, or photoperiod, also contributes to the process as a secondary signal, but it is the soil warmth that provides the necessary energy for cellular activity.
Geographical Differences in Spring Transition
Because the shift from dormancy to active growth depends on soil temperature, the timing varies significantly across the grass’s growing region. In the Deep South and along the Gulf Coast, where warm conditions arrive earlier, St. Augustine lawns typically begin to green up in late March or early April. In more inland or northern parts of the warm-season zone, such as central Texas or the upper regions of the Carolinas, the green-up may not occur until mid-April or even as late as mid-May.
This variability means that a fixed calendar date is less reliable than monitoring local soil temperatures. The risk of a late-season frost or cold snap can temporarily burn back new growth, causing the lawn to cycle between green and brown until stable warmth arrives.
Essential Lawn Care After Green-Up
Once the lawn is visibly greening up and requires regular mowing, it is time to transition from winter care to a spring maintenance schedule. Fertilization should be done approximately two to three weeks after the initial green-up, or after the lawn has been mowed twice. Using a slow-release nitrogen fertilizer, often with a nitrogen-phosphorus-potassium (N-P-K) ratio such as 3:1:2 or 4:1:2, is recommended. This application should deliver about \(0.5\) to \(1\) pound of actual nitrogen per \(1,000\) square feet of turf to support the burst of new growth.
St. Augustine grass performs best with deep, infrequent irrigation that encourages deep root development. The goal is to provide about one inch of water per week, either through rainfall or supplemental watering. Sandy soils may require more frequent, lighter applications to prevent the rapid drainage of moisture.
Initial mowing should begin as soon as the grass starts growing, set at a height of \(2.5\) to \(4\) inches. The higher end of the range is preferred for lawns in shaded areas or during periods of stress. Never remove more than one-third of the leaf blade in a single mowing session to prevent undue stress on the recovering turf.
Weed control requires careful timing, as St. Augustine grass is sensitive to many common herbicides, such as 2,4-D. Applying a pre-emergent herbicide to control summer annual weeds like crabgrass should occur when soil temperatures reach \(55^\circ\text{F}\) for several consecutive days. For existing weeds, post-emergent herbicides should only be applied after the lawn is fully greened up and actively growing, as application during the transition phase can severely damage the grass.