Fertilizer Schedule for St. Augustine Grass | Timing That Works

Fertilize St. Augustine grass three to four times per year, starting after full spring green-up and stopping before dormancy, with slow-release nitrogen at each feeding.

You can build an effective fertilizer schedule for St. Augustine grass around three simple timing windows: spring green-up, summer maintenance, and fall wind-down. The key is feeding the lawn when it can actually use the nutrients — not by a calendar date that may arrive weeks before or after your grass wakes up. University extension programs across the South agree on the same principles: start late, feed lightly through the growing season, and stop well before the first frost or local blackout period.

When To Start Fertilizing St. Augustine Grass

The single most common mistake is fertilizing too early. St. Augustine grass must be fully greened up and actively growing before it can use nitrogen. Applying fertilizer while the lawn is still partly dormant wastes money and can send nutrients into runoff. NC State Extension recommends waiting until at least May or two weeks after complete green-up — whichever comes later. In practice, that usually means late April in the Deep South and mid-to-late May farther north. A soil test done in early spring will tell you exactly what your lawn needs before you buy a bag.

How Much Nitrogen Your Lawn Actually Needs

St. Augustine grass needs 2–4 pounds of actual nitrogen per 1,000 square feet over the entire growing season, according to Clemson HGIC. Some sandy soils or longer growing seasons may push that toward 3–5 pounds, but the safer starting point is the lower end unless your soil test says otherwise.

Use a slow-release granular fertilizer with at least some water-insoluble nitrogen.

Following A Simple 3–4 Application Schedule

Split your annual nitrogen across three or four applications spaced through the growing season. Clemson’s program for the Carolinas calls for feeding in early May, again in June–July, and a third time before August 15, using a high-potassium blend for those summer rounds. NC State adds a lighter September application at half a pound or less per 1,000 square feet. For the fall window, switch to a higher-potassium product — your grass needs root strength, not leafy growth, heading into winter. If you’re shopping for the right product for that late-season feed, our top picks for fall St. Augustine fertilizer cover the ratios that work.

Regional rules matter. Florida counties enforce summer fertilizer blackout periods, typically pausing nitrogen during the rainiest months. Clay soils in the Piedmont region may only need two well-timed applications, while sandy soils in coastal areas often need the full four-feeding program. In every case, stop fertilizing when the lawn begins to enter dormancy — usually once nighttime temperatures stay below 65°F consistently.

FAQs

Can I use a weed-and-feed product on St. Augustine grass?

Weed-and-feed products are risky on St. Augustine because many contain herbicides that damage the turf, especially during spring green-up. If you need weed control, apply a St. Augustine-safe herbicide separately and at a different time than fertilizer. A straight fertilizer with slow-release nitrogen is generally safer.

What happens if I fertilize while the grass is dormant?

Fertilizing dormant St. Augustine grass feeds weeds instead of the lawn, and any nitrogen not taken up can leach into groundwater or run off into storm drains. Dormant roots cannot absorb nutrients efficiently, so the application is essentially wasted. Wait until you see at least 75% green coverage before the first feeding.

Should I water after applying fertilizer?

Yes — water the fertilizer in lightly right after application to move granules off the leaf blades and into the soil. Use about ¼ inch of water, enough to dissolve the granules without creating runoff. Heavy rain within 24 hours of application can wash nutrients away, so check the forecast before you spread.