St. Augustine Care: Mow High, Watch for Chinch Bugs

St. Augustine is the grass people choose when they have shade and want a southern lawn. It has the broadest blade and the most coarse texture of the common warm-season grasses, it spreads with thick above-ground runners, and it is managed almost exactly opposite to Bermuda — mow it high, not low.

On the weed side this grass is the most herbicide-sensitive common lawn grass in the country, and the sensitivity differs by cultivar — see best weed killer for st augustine before buying anything labelled for southern lawns.

What Makes St. Augustine Different

Four traits drive every care decision, and three of them differ from Bermuda:

• Coarse, broad blades. Distinctive and easy to identify — nothing else in a southern lawn looks like it up close.
• Thick above-ground stolons. It spreads across the surface with visible runners rather than knitting tightly at soil level. Good for covering ground, and the reason low mowing exposes and damages it.
• The best shade tolerance among warm-season grasses. This is its main selling point over Bermuda and the usual reason people pick it.
• No seed. Established only from sod, plugs or sprigs. Repairs cost money rather than a handful of seed.

In Texas, St. Augustine is grown alongside Bermuda, which is the dominant grass here. Mixed yards are common, and the two need opposite mowing heights — a single deck setting cannot serve both. Your USDA range is 6b–9b, and local soil reads: Texas holds nine of the twelve USDA soil orders — more than any other state, per Texas A&M — so "Texas soil" is not one thing. Three matter for lawns. The Blackland Prairie belt through Dallas, Waco and Austin is vertisol: Houston Black is the series, dark, clayey, high in pH, and what Texas A&M calls the state's unofficial state soil. East Texas around Houston and the Piney Woods is Ultisol — weathered loamy fine sands over a clayey subsurface, formed under forest and often acidic, which is why the pH advice flips as you drive east. West of the Pecos the soils are Aridisols carrying carbonate, gypsum and sodium chloride horizons, where salt in the profile and in the irrigation water is the limiting factor rather than texture..

Floratam and the other cultivars

Floratam is the most widely planted St. Augustine cultivar and the one most often named specifically on product labels. It is coarser and needs more sun than some alternatives, and it carries herbicide restrictions that a generic “St. Augustine” instruction may not cover. If you do not know your cultivar, treat label warnings about Floratam as applying to you until you find out.

NC State’s summary is worth having in one line before the maintenance detail: St. Augustinegrass “is a fast-growing turfgrass best adapted to the coastal plain” with “very coarsely textured leaves”, and it “spreads by stolons” — above-ground runners rather than underground ones. That last point explains most of what follows: everything it uses to spread is sitting on the surface where a low mower can reach it.

Mowing High Is Not Optional

The single most common failure is someone applying Bermuda habits to a St. Augustine lawn.

• Height: 3–4 inches. Floratam at the top of the range. Higher than most people expect.
• Never remove more than a third of the blade. At a 3.5 inch target, mow when it reaches about 5 inches.
• Sharp blade matters more here, not less — a coarse blade shreds visibly when the mower is dull, and the frayed tips brown across the whole lawn.
• Do not scalp. Scalping is a Bermuda practice. On St. Augustine it removes the leaf area the plant depends on and exposes stolons to sun scald.

Mowing high is also weed control: a tall, dense St. Augustine canopy blocks light from reaching the soil, and weed seeds cannot establish in the dark.

Feeding and Watering

St. Augustine is a moderate feeder — lighter than Bermuda — and the same warm-season timing rule applies: only while it is actively growing.

Your window in Texas is Late April after full green-up, June, and early September. Soil pH here reads: Alkaline (7.5–8.2) across most of the state, which locks iron away chemically — pale St. Augustine in this state is very often iron chlorosis rather than hunger, and chelated iron fixes it without forcing growth.

On watering, the drainage of your soil matters more than a fixed schedule:

Texas drainage reads: Two different soils depending on the week, and this is the single most useful thing to know about a Blackland lawn. Texas A&M defines the vertisol by its smectite clay, which "swells in size when wet and shrinks when dry", producing the surface cracking anyone in Dallas or Austin has seen in August. Practically: after a long dry spell the cracks swallow the first part of an irrigation cycle straight past the root zone, then the clay swells shut and sheds everything after it as runoff — so the same lawn measures as fast-draining and as sealed within one watering. Water in short repeated cycles rather than one long soak, and treat a percolation test done in drought as meaningless. East Texas sands drain genuinely fast and leach nitrogen instead; the far west drains fast to caliche or a salt pan.. Fast-draining soil means more frequent but still deep watering, and split fertilizer doses since nitrogen leaches quickly.

Chinch Bugs: The Signature Pest

If a St. Augustine lawn is browning in summer, chinch bugs are the first suspect. They are strongly associated with this grass.

How to recognise it:

• Damage starts in the hottest, sunniest strip — beside a driveway, a south-facing wall, a curb — and expands outward in heat waves.
• The turf yellows, then browns, and does not green up with watering.
• The pull test stays firm. Chinch bugs feed on stems and crowns, not roots, so the turf does not lift like a rug. That is what separates them from grubs.
• Part the grass at the margin of a damaged area and watch the soil line for small moving insects.

Drought damage looks similar and is the usual misdiagnosis. The difference is that drought yellowing follows your irrigation coverage, and it recovers when you water deeply. Chinch bug damage does not.

Our chinch bug guide has the float test that confirms it in five minutes, and the documented insecticide resistance that decides what is worth buying. The other Southern lawn pest worth knowing is not a grass feeder at all — fire ants build mounds instead, and the fix is bait rather than anything sprayed on the turf.

Texas Lawn Threat Matrix

What to scout for on Bermuda lawns in USDA zones 6b–9b.

High-Risk Weeds

• Crabgrass
• Dallisgrass
• Nutsedge
• Henbit
• Spurge
• Grassbur (sandbur)
• Rescuegrass

High-Risk Diseases

• Brown patch / large patch
• Take-all root rot
• Gray leaf spot (St. Augustine)
• Dollar spot
• Spring dead spot (Bermuda)

Common Pests

• Chinch bugs
• White grubs (June beetle larvae)
• Fire ants
• Fall armyworms
• Bermudagrass mites

The Texas St. Augustine Year

Generic calendars are less useful than your own. For Texas — Spring and fall peaks (May and October); prolonged summer drought with 95–105°F heat — extension guidance for this climate runs:

• Spring: Apply pre-emergent by mid-March (soil temp 55°F)
• Spring: Scalp and bag Bermuda once at green-up to remove dormant thatch
• Spring: First fertilization after 100% green-up — never earlier
• Spring: Aerate compacted clay soils April–May
• Summer: Water deeply and infrequently (1 inch/week, respecting local watering schedules)
• Summer: Raise mowing height during drought stress
• Summer: Avoid herbicide applications above 90°F — turf injury risk
• Summer: Treat fire ant mounds with bait products in early summer
• Fall: Apply fall pre-emergent by early September for winter weeds
• Fall: Fertilize warm-season turf 4–6 weeks before first frost
• Fall: Watch for brown patch in St. Augustine as nights cool

For patching, note that St. Augustine cannot be seeded — plan sod or plugs inside your local establishment window: May–July for Bermuda; avoid establishment during August heat. Local last frost: Mid-March (Dallas) to mid-February (Houston/San Antonio).

The Herbicide Problem

This is where St. Augustine lawns die, and it deserves its own section.

Several common broadleaf herbicides that are routine on Bermuda will injure or kill St. Augustine, and Floratam is singled out by name on many labels. Atrazine-based products are widely used on St. Augustine precisely because the standard three-way mixes are risky on it.

Three rules, none of them optional:

1. The label must name St. Augustine. Not “southern lawns”, not “most grasses” — St. Augustine, and ideally your cultivar.
2. Respect the temperature ceiling. Most turf herbicides injure grass above roughly 85–90°F, and St. Augustine has less margin than Bermuda does.
3. Spot-treat rather than blanket-spray. Less product, less risk, same result on scattered weeds.

Our lawn weed identification guide covers matching the weed family to the right product family before you buy anything, and how to kill dandelions without killing grass walks the selective-herbicide basics.

The Care Plan

Products for a St. Augustine Lawn

One piece of good news on this grass: gray leaf spot names St. Augustine constantly, but NC State ranks it the MOST resistant host — rarely badly damaged when it is managed.

And the weed that most often follows over-watering on this grass has its own page — dollarweed, where the first fix is the irrigation and the herbicide table is sorted by grass.

Use that last one only once you have confirmed the insects, not as insurance. It treats the entire lawn, and the bifenthrin in it is toxic to bees and aquatic life — so it belongs on a lawn with a real problem, kept off blooming weeds and away from drains. If you only need to feed, feed.

Note what is not here: a general-purpose three-way broadleaf herbicide like Weed B Gon. On St. Augustine, applying common herbicides blind is how lawns get killed. The Texas A&M herbicide tolerance table lists Quinclorac as “NR” (Not Recommended) for St. Augustine, and common actives like 2,4-D and dicamba as “C” (Caution). The only fully “T” (Tolerant) consumer active is Atrazine. Identify the weed first, then find an Atrazine-based product or confirm the label specifically names your St. Augustine cultivar.

If you are considering a robotic mower, check its maximum cutting height first: UF/IFAS notes most were designed for grasses mowed below 2.5 inches, while St. Augustine wants 2.5–4. Robot mowers on St. Augustine grass covers UF’s trial at 2.4 inches and the delayed dormancy that came with it.

If a patch thins in the same place each spring and the runners lift off the soil like a rug, that is not drought — take-all root rot covers the field test that separates it from large patch and chinch bugs, and why fungicide sprayed on a visible patch does nothing.