St. Augustine Fertilization Timing and Rates for DFW Lawns

St. Augustine grass is the most common lawn in North Texas — and the most commonly overfed one. Homeowners see a pale, thin lawn and reach for a bag of fertilizer, not realizing that the timing is as important as the product. Feed St. Augustine at the wrong time and you get lush, soft growth that draws chinch bugs and fungal disease. Feed it at the right time with the right rate, and you get a thick, dense carpet that shuts out weeds and handles summer heat without flinching. We’ve been dialing in fertilization programs for Arlington and DFW lawns since 2006, and St. Augustine timing is one of the topics we get asked about most.

How St. Augustine Grows in North Texas

St. Augustine (Stenotaphrum secundatum) is a warm-season grass that spreads exclusively by stolons — above-ground runners that creep across the soil surface. It has no underground rhizomes, which means it depends entirely on healthy stolon growth to fill in thin spots and hold territory against weeds. Stolons need consistent nutrition to grow vigorously, but St. Augustine is also considerably more sensitive to over-application than Bermuda. Too much nitrogen too fast produces the kind of soft, lush growth that fungal pathogens love.

In DFW, St. Augustine breaks dormancy later than Bermuda — typically when soil temperatures reach 65–70°F consistently, which lands somewhere between late March and mid-April depending on the year. It remains actively growing through October before going fully dormant with the first hard frost. The active growing season runs roughly 7 months, but the windows for effective fertilization are narrower than most homeowners think.

The Spring Fertilization Window

The most important rule for St. Augustine fertilization: do not apply nitrogen before the lawn is fully green and actively growing. Feeding a lawn that is still transitioning out of dormancy is wasteful at best and harmful at worst. Nitrogen sitting in cold, barely-active soil either leaches through without being absorbed or promotes disease pressure on tissue that isn’t healthy enough to handle it.

Wait until the lawn is at least 75% green and actively growing — usually late April to early May in Arlington. Then apply a balanced starter fertilizer with a complete NPK ratio. For St. Augustine, an ideal spring application delivers roughly:

• 1 lb of actual nitrogen per 1,000 sq ft as the first application of the season
• Phosphorus included only if a soil test indicates deficiency (DFW clay soils are often already high in phosphorus)
• Potassium at a moderate rate to support root development and stress tolerance

Slow-release nitrogen products — particularly those using polymer-coated urea — are strongly preferred for St. Augustine because they minimize the spike-and-crash growth cycle that creates disease vulnerability.

Summer Feeding: Less Is More

St. Augustine doesn’t need the aggressive summer nitrogen program that Bermuda demands. In fact, heavy nitrogen applications in July and August on St. Augustine are one of the leading causes of gray leaf spot outbreaks in DFW lawns. The fungus thrives in the hot, humid conditions that coincide with heavy summer nitrogen feeding.

A responsible summer fertilization approach for St. Augustine looks like this:

• Iron supplementation instead of or alongside reduced nitrogen — iron greens up St. Augustine fast without driving soft growth
• No more than 0.5–0.75 lbs of actual nitrogen per 1,000 sq ft if a nitrogen application is warranted
• Skip applications entirely during prolonged heat waves above 100°F or when the lawn is drought-stressed

The best-looking St. Augustine lawns in Arlington during summer are often the ones that got less fertilizer, not more. A lawn that stays consistently dark green without excess growth is a healthy lawn — not an underfed one.

Fall Fertilization: Potassium Is the Priority

As temperatures drop and days shorten heading into September and October, St. Augustine shifts its energy from top growth to root development and carbohydrate storage — both of which fuel a faster, healthier green-up the following spring. This is the time to apply potassium, not nitrogen.

A fall potassium application (often called a “winterizer” program) typically delivers:

• 1–1.5 lbs of potassium per 1,000 sq ft using a high-potash formulation like 0-0-50 or similar
• Minimal or no nitrogen — late-season nitrogen pushes new growth that can’t harden before frost
• Application timing before first expected frost — in DFW, this means September through mid-October

Skipping the fall potassium application is one of the most common mistakes we see on St. Augustine lawns. Homeowners who invest in fall potassium consistently see faster spring green-up and better color through the following growing season.

Soil pH and Fertilizer Efficiency

North Texas is notorious for alkaline clay soils with pH values frequently running between 7.5 and 8.2. St. Augustine prefers a soil pH of 6.0–7.0, and outside that range, nutrient uptake suffers even when the right fertilizer is applied. Iron chlorosis — the yellowing of grass blades despite adequate nitrogen — is almost always a pH-related issue on DFW lawns, not a true iron deficiency in the soil.

Chelated iron products sidestep this problem by delivering iron in a form that remains available at alkaline pH levels. Sulfur applications can incrementally lower soil pH over time, but this is a multi-year process and rarely fully corrects the DFW alkalinity problem. Regular foliar iron applications are the most practical tool for maintaining St. Augustine color in our region.

Annual Nitrogen Totals: Stay in Range

The Texas A&M AgriLife Extension recommends a total annual nitrogen input for St. Augustine of 2–4 lbs per 1,000 sq ft, distributed across the growing season. Most DFW homeowners applying fertilizer themselves are either applying too much total nitrogen or applying it at the wrong times. The professional approach is to spread that annual total across 3–4 targeted applications aligned with the lawn’s growth cycle rather than hitting a fixed calendar date.

For the full picture of how we structure weed control and fertilization programs for St. Augustine and other North Texas turf types, visit our weed control and fertilizer services page. And if you want to understand what herbicides are safe — and unsafe — on St. Augustine, our follow-up post on weed control challenges specific to Bermuda grass provides useful comparison context for how different turf types handle chemistry differently.