St. Augustine Lawn Care Guide for Texas

Nitrogen Budget

For St. Augustinegrass, the general nitrogen budget for the year runs from about 0.5 lb to 3.5 lb of nitrogen per 1,000 square feet, applied across the growing season rather than in one dose. Push much past 5 lb per 1,000 square feet and you're outside the range this guide considers reasonable — more nitrogen doesn't make a better lawn, and it can outrun what the grass can use. Split the total across the fertilizer windows below rather than putting it all down at once.

Mowing Height by Season

Keep St. Augustine in the 3 to 4 inch mowing band through spring, summer, and fall, with 3.5 inches as the target — that height sits in the sweet spot for density without scalping.

Whatever the height, follow the one-third rule: never remove more than one-third of the blade in a single mow. If the lawn has gotten away from you, step the height down gradually over two or three mows instead of scalping it back in one pass.

The Seasonal Schedule

Apply a pre-emergent herbicide in the window from March 1 to March 29, timed to when soil temperature rises through 55°F, to get ahead of summer annual weeds before the lawn fills in.

Once soil is consistently above 65°F and the lawn shows around 50% green-up, typically April 6 to May 4, put down the first fertilizer application of the year. Core aeration fits shortly after, April 24 to June 5, once the lawn is actively growing with soil above 65°F and 75% or more green-up.

St. Augustinegrass has no viable commercial seed, so bare or thin spots get filled with plugs or sod rather than seed. That window runs May 4 to June 29, once soil warms through 70°F, giving new plugs a full season to knit in before fall. Keep them well watered until established.

Broadleaf weeds are best treated May 1 to June 18, once the lawn has fully greened up, using a post-emergent herbicide labeled for St. Augustine. Some broadleaf herbicides injure St. Augustine and centipede, so confirm the label lists your grass before applying, and avoid spraying above roughly 90°F or when the lawn is under drought stress. The label is the law.

Early summer, May 11 to June 22, is the window for a preventive grub control if you need one — most lawns don't. Treat only if you've had grub damage before or grubs are a known problem in your area; otherwise scout for damage rather than treating on a calendar.

Peak-growth feeding runs May 25 to July 6, then again July 15 to August 26 as the last heavy nitrogen application before the fall transition. A wetting agent applied May 16 to July 15 helps water soak in rather than bead up and run off through the hottest stretch, and can be reapplied through summer as needed.

As soil cools through 70°F, typically August 28 to October 3, a pre-emergent herbicide stops winter annual weeds — annual bluegrass, henbit, chickweed — before they germinate in the dormant or semi-dormant lawn. This product also blocks grass seed, including any winter ryegrass overseed, so it's one or the other, not both. Confirm the product is labeled for St. Augustine.

A high-potassium, low-nitrogen application from September 30 to November 11 builds cold hardiness before dormancy, and soil samples pulled July 27 to October 25, while the lawn is still active, let the results guide any lime or nutrient adjustments.

Watering

Aim for about ¾ inch of water a week, split into two deep soakings of about ½ inch each, watered early in the morning. That target rises in sustained heat — add roughly a quarter inch when highs run near the mid-80s, and up to about a half inch more when three or more days push near 90°F, capped so the soil can absorb it without runoff. Watering deep and infrequent encourages roots to grow down, and morning watering lets the lawn dry before night, since wet grass overnight invites disease.

Product Timing Conflicts

A few product categories carry timing rules worth keeping in mind if you're planning to seed anything, such as overseeding with winter ryegrass. If you've recently applied a broadleaf herbicide, wait about 6 weeks (42 days) before seeding. If you've recently put down a crabgrass pre-emergent, wait about 12 weeks (84 days) before seeding, since these products are built to stop germination and will work against grass seed just as they work against weeds.

Since St. Augustine itself is established from plugs or sod rather than seed, these waiting periods matter most for any seeded overseed you're planning — build the calendar around them rather than layering products back to back.

Texas summers ask a lot of a lawn, and the schedule above is a framework, not a script. Watch the grass and the soil temperature more than the calendar, and always check the product label before applying anything.