St. Augustine grass care: the complete guide

If you've got a thick, blue-green carpet of lawn anywhere along the Gulf Coast or down in Florida, chances are it's St. Augustine grass — and it plays by its own rules. It's the most popular lawn grass across the humid South for good reason: it's lush, it shrugs off heat and salt, and it tolerates more shade than almost any other warm-season grass. But it's also fussy about a few specific things, and getting one of them wrong (looking at you, weed killer) can wreck a lawn fast. This guide walks you through St. Augustine grass care the friendly way — what it is, how to mow, water and feed it, and how to spot trouble before it spreads.

What St. Augustine grass actually is

St. Augustine (Stenotaphrum secundatum) is a coarse-textured warm-season grass with wide, flat, broad blades — noticeably chunkier than Bermuda or zoysia. You don't grow it from seed; it spreads by stolons (above-ground runners) that creep sideways and root as they go. That's why you plant it as sod or plugs and let it fill in.

A few things make it special:

• Shade tolerance. It's the go-to grass for yards with tree cover. It handles filtered shade better than any other Southern grass, though it still wants 4+ hours of sun a day.
• Salt tolerance. It thrives near the coast where salt spray would burn other lawns.
• Fast horizontal spread. Those runners knit bare patches together quickly in warm weather.
• No cold hardiness. It browns off in frost and won't survive true Northern winters, which is why you see it from Florida across to Texas and up into the Carolinas, but not much further north.

Mowing: keep it tall

Here's the single most common mistake — people scalp St. Augustine like it's a golf green. Don't. It's one of the tallest-cut lawn grasses out there.

The key insight: St. Augustine grass wants to be mowed at 2.5 to 4 inches (6.5–10 cm) — much higher than Bermuda or zoysia. Cutting it short weakens the runners, invites weeds, and leaves it wide open to its worst pest, the chinch bug. In shade, mow at the very top of that range.

• Mow at 3–4 inches (7.5–10 cm) for most lawns; go to the 4-inch (10 cm) end in shady areas so blades capture more light.
• Follow the one-third rule. Never remove more than a third of the blade in one cut. If it's overgrown, bring it down over two or three mowings.
• Keep the blade sharp. Those broad blades tear and brown at the tips with a dull mower.
• Leave the clippings. They break down fast and return free nitrogen — this isn't the same as thatch.

Watering

St. Augustine likes water but hates soggy feet. The goal is deep, infrequent soaking rather than daily sprinkles.

• Aim for about 1 inch (2.5 cm) per week, including rainfall, split into one or two sessions.
• Water early morning (4–9 am) so blades dry through the day — wet overnight foliage is fungus fuel.
• Watch the grass, not the calendar. Blades that fold, turn blue-grey, or hold your footprints are telling you it's thirsty.
• Ease off in winter when the grass is semi-dormant and using far less.

Fertilising schedule

St. Augustine is a moderate-to-heavy feeder during the growing season and needs almost nothing while dormant. Feed it while it's actively green and growing — roughly April through September in most of the South.

• Wait for real green-up in spring. Feeding too early pushes tender growth that frost can burn.
• Use slow-release nitrogen to avoid the thatch and disease that come with growth surges.
• Reach for iron (chelated) supplements if the lawn looks pale but is growing fine — often it's iron, not nitrogen, it wants.

Common problems (and what causes them)

Chinch bugs — public enemy number one

Chinch bugs are St. Augustine's signature pest. They pierce the blades and suck out sap, leaving irregular yellow-to-brown patches that spread outward, usually in the hottest, sunniest, driest part of the lawn in mid-summer. It's easy to mistake for drought.

• Confirm before you treat. Part the grass at the edge of a dying patch and look for small black-and-white insects, or do the "float test" with a bottomless can pushed into the soil and filled with water.
• Treat with bifenthrin or another labelled pyrethroid; keep the lawn healthy and not over-fertilised, since lush thatchy grass makes it worse.

Fungal diseases

• Brown patch / large patch (Rhizoctonia) — large circular brown rings in cool, wet spring and autumn. Ease off nitrogen and water in the morning only; treat with azoxystrobin if it spreads.
• Gray leaf spot — grey-brown spots with dark borders on the blades in hot, humid summer weather, worse where nitrogen is high. Cut back feeding and improve airflow.
• Take-all root rot — thinning, yellowing patches with rotten roots that don't respond to water or fertiliser. Lower the soil pH, avoid stress, and improve drainage.

Thatch

St. Augustine can build a spongy thatch layer from its runners, especially if over-fed and over-watered. If it's over about half an inch (1.3 cm), the lawn feels bouncy and sheds water. Don't dethatch aggressively with a power rake — it can shred the stolons. Core aeration and easing off nitrogen is the gentler fix.

Weed control — read this before you spray

This is where St. Augustine catches people out. Many common lawn herbicides that are safe on other grasses will injure or kill St. Augustine.

• Avoid quinclorac entirely. It's a popular crabgrass killer that damages St. Augustine — check every product label for it.
• Be cautious with 2,4-D and MCPP, which can burn St. Augustine, especially in heat. Use reduced rates and never spray above about 85°F (29°C).
• Atrazine is a mainstay for St. Augustine weed control and is generally safe on it — but it's restricted or banned in some states and counties, so check local rules before buying.
• Always confirm the label lists St. Augustine (or Floratam) by name. A "safe for lawns" claim is not enough.
• Prevent weeds the easy way — mow tall and feed properly. A dense, 4-inch (10 cm) St. Augustine canopy chokes out most weeds on its own.

Choosing a variety

• Floratam is the classic sun-loving choice but needs open, bright yards.
• Palmetto is the safest pick if you've got mixed sun and shade.
• Raleigh buys you a bit more cold resistance for the northern edge of St. Augustine country.

Frequently asked questions

How often should I mow St. Augustine grass?

Usually once a week during the growing season, keeping it at 3–4 inches (7.5–10 cm). In peak summer it may need cutting every 5–6 days; in winter dormancy it barely grows at all.

Why is my St. Augustine grass turning yellow?

The three usual suspects are iron deficiency (add chelated iron), chinch bugs (check for insects in the sunniest patches), or overwatering. If it's pale but growing, suspect iron; if patches are dying and spreading in the heat, suspect chinch bugs.

Can I use regular weed killer on St. Augustine grass?

No — many won't work safely. Quinclorac damages it, and 2,4-D can burn it in heat. Only use products that name St. Augustine on the label, and check whether atrazine is legal in your state.

What's the lowest I can mow St. Augustine?

Around 2.5 inches (6.5 cm) for varieties in full sun, but most lawns do better at 3–4 inches (7.5–10 cm). Mowing shorter than that stresses the runners and invites pests and weeds.

How Lawnova takes the guesswork out of St. Augustine

St. Augustine care is mostly about timing — feeding at green-up, treating chinch bugs before they spread, and never reaching for the wrong herbicide. Lawnova builds you a personalised calendar based on your grass type, your variety and your local climate, then nudges you when it's time to mow, water, feed or scout for pests, so you're never guessing. It even flags which weed products are safe for St. Augustine in your state.

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Grow it tall, feed it right, and that carpet will look after itself.