San Antonio's spring comes early and moves fast. The line between last winter cold snap and full-on summer heat is narrow, maybe six weeks, and the decisions you make in that window have a bigger effect on your lawn than anything you do in summer. Get the pre-emergent down late and you spend the whole season fighting summer weeds. Fertilize before the grass is actively growing and you waste product and feed the weeds instead. The sequence below is built around the actual timing for Bexar County.
Quick answer
In San Antonio, the spring lawn care sequence is: apply a pre-emergent for crabgrass and summer annuals when soil temperatures reach 55-60 degrees (typically late February to mid-March), wait for active green-up before fertilizing with nitrogen, and mow the first two cuts at a lower height to remove dead leaf tissue before raising back to your normal setting. Do not fertilize dormant grass. Wait for the grass to tell you it is growing before you push it.
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Pre-Emergent First, Before Weeds Germinate
The most important spring lawn care move is applying a pre-emergent herbicide before summer annual weeds germinate. Crabgrass and other warm-season weeds begin sprouting when soil temperatures at the two-inch depth reach 55 to 60 degrees Fahrenheit for several consecutive days. In San Antonio, that typically happens somewhere between late February and mid-March depending on the year.
Pre-emergent works by creating a chemical barrier in the top inch or two of soil that prevents seeds from rooting. Once a weed has already sprouted, pre-emergent does nothing. The timing window is firm, and catching it matters more than which product you use. Soil thermometers are inexpensive and worth using. The Texas A&M turf team publishes soil temperature data for San Antonio that is a reliable reference.
Wait for True Green-Up Before Fertilizing
St. Augustine and Bermuda grass break dormancy based on soil temperature and day length, not calendar date. In a warm year that can mean mid-February color. In a cool spring it can drag into late March. Applying nitrogen fertilizer to a lawn that is still dormant or barely stirring is wasteful, and it can invite a late weed flush that your thin, just-waking grass isn't yet equipped to crowd out.
The right cue is visible: two to three weeks of consistent new green growth, lawns filling in uniformly, no significant brown dormant patches. That is when the grass has established root activity and can use nitrogen to build leaf and root mass. A starter-level nitrogen application at this point, around 0.5 to 0.75 pounds of nitrogen per 1,000 square feet, gets things moving without pushing excessive growth early.
The First Two Mowings
St. Augustine coming out of dormancy has a layer of dead tan leaf tissue at the top that the new growth is pushing through. The first one or two mowings of the year at a slightly lower height than your normal setting removes that dead material and lets light reach the new growth. Drop one notch below your usual mowing height for the first cut, then return to your standard setting.
This is not scalping. Scalping means cutting so short you remove living tissue and expose the crown, which sets the lawn back. The goal is just to clear the accumulated dead thatch cap from winter, not to cut deep into the plant. If the lawn looks uniformly green without much dead material after a mild winter, skip the low cut and start at normal height.
- Late February to mid-March: apply pre-emergent before soil temps hit 60F
- When grass shows 2-3 weeks of new growth: first nitrogen application
- First 1-2 mowings: one notch lower than normal to clear winter debris
- After green-up: return to standard mowing height and schedule
What to Skip in Spring
Avoid post-emergent broadleaf herbicides while St. Augustine is breaking dormancy and in active flush. The grass is stressed enough managing the transition from dormancy and is more sensitive to herbicide phytotoxicity than it will be in June. If you have broadleaf weeds in spring, hand pull where the pressure is light or wait until the grass is fully established and growing vigorously before spraying.
Also skip heavy aeration in early spring. Aeration works best when the grass has enough growing season ahead to fill the holes. March aeration in San Antonio is borderline. If you're going to aerate once a year, late spring after green-up is complete or early fall are both better windows.
Reading the Lawn Before You Treat
Spring is a good time to walk the lawn and identify thin areas, bare patches, or zones with persistent weed pressure. Those spots usually tell you something: a buried irrigation leak, a compaction zone where foot traffic concentrates, an area with a different soil profile. Treating symptoms without understanding the cause tends to produce the same result next year.
If you have patches that greened up later or more thinly than the rest, note their location. They are often the same spots that struggled last summer. Understanding the pattern is what makes a lawn care prescription actually work.