St. Augustinegrass Lawn Care Guide for Louisiana

Nitrogen Budget

For St. Augustinegrass in Louisiana, the general nitrogen range for the season sits between 0.5 and 3.5 lbs of nitrogen per 1,000 square feet, with 5 lbs per 1,000 square feet marking the point where more is doing more harm than good. Split that total across the season's feedings — a spring green-up application, one or two summer applications during peak growth, and a fall potassium-heavy, low-nitrogen application to harden the lawn for winter — rather than putting it all down at once.

Mowing Height Through the Seasons

St. Augustinegrass holds up best kept in a 3 to 4 inch band, and in Louisiana that means aiming for around 3½ inches through spring, summer, and fall alike — the sweet spot for density without scalping. When the lawn gets away from you, don't cut it straight back down: step the height down gradually over two or three mows, never removing more than a third of the blade in a single pass.

The Season Ahead

The first big soil-driven trigger of the year is a pre-emergent herbicide window running Mar 1 to Mar 29, timed to soil temperatures rising through 55°F to get ahead of summer annual weeds before they germinate. As soil warms further and roughly half the lawn has greened up, a spring green-up fertilizer application follows, generally Apr 6 to May 4, once soil holds consistently above 65°F.

Because St. Augustinegrass has no viable commercial seed, filling in bare or thin patches means plugs or sod rather than seed — best done May 4 to Jun 29, once soil rises through 70°F and the grass is actively growing enough to knit in before fall. That window overlaps with an early-summer grub preventive period, May 11 to Jun 22, worth watching for only if grub damage has been a recurring problem in your lawn or area — most lawns can skip it and just scout. It also overlaps a broadleaf weed control window, May 1 to Jun 18: St. Augustine can be sensitive to some broadleaf herbicides, so confirm the label lists your grass before spraying, and avoid application above roughly 90°F or during drought stress.

Summer carries two more fertilizer windows — one centered in June (May 25 to Jul 6) and another in late summer (Jul 15 to Aug 26) — plus a wetting agent application, May 16 to Jul 15, to help water soak in rather than bead off during the hottest stretch. As soil cools back through 70°F in fall (Aug 28 to Oct 3), a fall pre-emergent targets winter annual weeds like annual bluegrass, henbit, and chickweed — but it will also block grass seed, including any winter ryegrass overseed, so plan for one or the other, not both. Round out the year with a fall potassium application, Oct 10 to Nov 21, to build cold hardiness, and an annual soil test, Jul 27 to Oct 25, to guide next year's adjustments.

Watering

Aim for about ¾ inch a week, split into two deep soakings of about ½ inch each, watered early in the morning so the lawn has time to dry before nightfall — wet grass overnight invites disease. In sustained heat, that target climbs: roughly a quarter inch more once highs sit near the mid-80s, up to about a half inch more when three or more days push near 90°F, capped so the soil can actually absorb it rather than running off.

Timing Conflicts to Keep in Mind

If you've recently applied a broadleaf herbicide, wait about six weeks (42 days) before seeding. If you've recently put down a crabgrass pre-emergent, wait about twelve weeks (84 days) before seeding. Since St. Augustinegrass itself establishes from plugs or sod rather than seed, these waiting periods mainly matter if you're overseeding with a cool-season grass such as ryegrass for winter color — worth planning any herbicide or pre-emergent application around that gap. Always confirm timing and grass compatibility on the product label — the label is the law.

None of this needs to be exact to the day — soil temperature and how the lawn is actually responding matter more than the calendar. Use these windows as a general guide, watch the grass itself, and confirm details on the product label before applying anything.