St. Augustine Weed & Feed (Fertilizer Guide)

For St. Augustinegrass, use weed-and-feed only when its label names your grass and the weeds you want to control. Apply during active growth, at the labeled rate, and under the stated weather and watering conditions. Count its nitrogen toward your yearly plan. There is no safe universal product rate or spreader setting.

A bag labeled “southern lawn” or “warm-season grass” is not automatically safe for St. Augustinegrass. Some herbicides can injure this turf, especially when it is stressed, newly planted, or treated in hot weather. The product label is the rulebook: it determines whether the product fits your grass, weeds, timing, and site.

I start with three checks before considering a combination product: Is the weed correctly identified? Does the label list St. Augustinegrass? Does the lawn need nitrogen now? If any answer is unclear, pause. A separate weed treatment or a local soil-test recommendation may be a better fit.

Product Selection, Turf Compatibility & Safety Preparation

A weed-and-feed product combines fertilizer with a weed-control ingredient. Its convenience does not make every formula suitable for every lawn. Check the full label for St. Augustinegrass, your target weeds, rate limits, temperature guidance, and directions for watering, mowing, and keeping people and pets off treated areas.

Check the grass, weeds, and active ingredient

“Active ingredient” means the chemical in the product that controls weeds. Read the label’s turf list and weed list, not just the front of the bag. A product approved for another warm-season grass is not automatically safe for St. Augustine. Also check for cultivar limits; Floratam and other cultivars may have specific restrictions.

Identify the weed before buying. Broadleaf weeds, such as some clovers, differ from grassy weeds, and a product labeled for one group may not control another. If you cannot identify the plant, take a clear photo or sample to your county extension office. Avoid guessing from a picture alone when the lawn is at risk.

Next, review the label’s restrictions for temperature, newly established turf, reseeding or sod, and nearby plants. Some products have limits that vary by active ingredient and formulation. Do not rely on a general rule or another product’s directions.

Decide whether combination treatment makes sense

A weed-and-feed treatment can be useful when the lawn has labeled broadleaf weeds and is ready for a measured fertilizer application. It can be a poor fit when only a few weeds are present, the lawn does not need nitrogen, or label directions do not match the site. In those cases, treating weeds separately may avoid adding fertilizer you do not need.

The annual nitrogen plan matters. A common warm-season maintenance range is about 2–4 pounds of actual nitrogen per 1,000 square feet per year, split across applications during active growth. Soil tests and local extension guidance should shape the plan. Count nitrogen from every fertilizer product, including weed-and-feed.

Set up safely

Measure the lawn area you plan to treat, excluding beds, paved areas, and other places the label says to avoid. Check the weather and nearby drains, ponds, and desirable plants. Keep granules out of storm drains and water. Wear any protective gear the label requires, and do not fill a spreader over a driveway where spilled product could wash away.

Calibrated Application and Post-Treatment Care

Calibration means checking how much product your spreader applies over a known area. It helps prevent both missed strips and excess doses. Use the product’s labeled rate and directions, then verify your equipment with a measured test. Do not copy a setting from a different product, even if the spreader brand is the same.

Calculate the amount before opening the bag

The label rate controls. If you are checking how much product would supply a chosen amount of nitrogen, use:

Product pounds per 1,000 square feet = desired nitrogen pounds per 1,000 square feet ÷ nitrogen percentage as a decimal

For example, a 20% nitrogen product contains 0.20 pounds of nitrogen per pound of product. Supplying 0.5 pound of nitrogen per 1,000 square feet would take 2.5 pounds of that product per 1,000 square feet. That calculation does not authorize the application. Use it only if the product label permits that rate and use on St. Augustinegrass.

Find the product quantity for your measured lawn area from the label rate. If the label rate is given per 1,000 square feet, multiply it by the treated area in square feet and divide by 1,000. Do not exceed the labeled rate to reach a fertilizer target.

Calibrate the spreader and apply evenly

Use the labeled spreader setting only as a starting point, if one is provided for your model. To check delivery, apply product over a measured test area on turf where the label permits use, then catch and weigh the amount dispensed. Adjust and repeat until the output matches the label rate. Do not make the test on pavement or where granules could enter a drain.

Follow the label’s application pattern. Control the spreader at edges, avoid overlap, and do not apply when wind could carry granules into beds or water. Sweep stray granules from hard surfaces back onto the lawn if the label allows. Do not double-treat a missed strip by making an extra full pass; use the label’s directions to correct coverage safely.

Follow the product’s activation directions

Granular products do not all work the same way. Some labels call for application to moist foliage and a rain-free period afterward. Others direct you to water the product in. These instructions are not interchangeable. Check the exact product label for foliage moisture, rainfall, irrigation, and rain-free timing.

The same applies after treatment. Follow label directions for re-entry, pets, mowing, and irrigation. Record the product name, active ingredient, rate, date, and treated area. That record helps you avoid an accidental repeat application and gives you useful details if the lawn shows stress.

Nutrient Planning, Mowing and Weed-Control Follow-Up

St. Augustinegrass needs fertilizer only as part of a season-long plan, not simply because weeds are visible. Nitrogen is the nutrient most often highlighted in lawn fertilizer; the percentage on the bag shows its share by weight. Keep a running total from all products, and use local soil-test and extension advice to set the plan.

Time fertilizer for active growth

Apply after spring green-up, while the grass is actively growing, and within local extension recommendations. Do not fertilize dormant or drought-stressed turf. Avoid late-season nitrogen when it could delay the grass’s hardening before cold weather. Local climate and extension guidance matter because growing seasons differ.

If the lawn is yellow, thin, or slow to grow, do not assume it needs more nitrogen. Poor drainage, pests, disease, mowing height, or other nutrient issues can also affect turf. A soil test can help clarify nutrient needs. It does not replace checking the herbicide label for safe use.

Mow at the right height and wait as directed

Mowing height depends on cultivar and local guidance. A common range for St. Augustinegrass is roughly 2.5–4 inches, with some cultivars, including Floratam, commonly kept toward the higher end. Do not cut the lawn too short just to make an application easier. If you mow before treatment, follow the product’s waiting period before mowing again.

Learn from two common lawn scenarios

These examples are decision guides, not reports of specific properties. They show how the same product can be suitable in one situation and a poor choice in another.

Scenario 1: Active lawn, labeled weeds. A homeowner sees broadleaf weeds in a green, actively growing St. Augustine lawn. The label lists both St. Augustinegrass and the weeds, and its timing and weather limits fit current conditions. The homeowner measures the area, checks the annual nitrogen total, calibrates the spreader, and follows the label’s activation and re-entry directions. This is a case where a combination product may fit.

Scenario 2: Heat stress and uncertain weed identity. Another lawn is dry and showing stress, and the homeowner cannot tell whether the plants are broadleaf or grassy weeds. Applying a generic weed-and-feed could add unneeded nitrogen and expose the turf to an unsuitable herbicide. The safer next step is to identify the weed, address water stress, and consult the label and local extension guidance before treating.

After application, give the product time to work as directed. Do not repeat treatment simply because weeds remain visible right away. Check the label for any repeat-treatment interval, and watch the grass for discoloration or other injury. If turf damage appears, stop further applications and seek guidance from the product maker or a local extension office.

Seasonal Timing, Storage and Environmental Protection

Good timing protects both the lawn and nearby plants and water. Apply only when the grass, weather, and site meet label directions. Store leftover product in its original container, closed and dry, and follow label instructions for storage and disposal. Never pour unused product or rinse water into a storm drain.

Use this pre-application checklist

• Confirm the product label names St. Augustinegrass and the target weeds.
• Check cultivar limits, temperature range, turf establishment rules, and any site restrictions.
• Confirm the lawn is actively growing and not drought-stressed.
• Measure treated area and calculate product quantity from the labeled rate.
• Calibrate the spreader; do not guess or borrow a setting.
• Check the required foliage, rain, irrigation, mowing, and re-entry instructions.
• Keep granules away from drains, water, beds, and other areas excluded by the label.
• Record the product, rate, area, and date.

The practical rule is simple: do not apply unless the exact product label permits use on your turf under current conditions. When that is not clear, wait and verify rather than risk turf injury.

FAQ

Can I use any weed-and-feed product on St. Augustinegrass?
No. Use only a product whose label permits application to St. Augustinegrass and lists the weeds you want to control.

When should I apply weed-and-feed to St. Augustinegrass?
Apply only after spring green-up, during active growth, and within local guidance and the product’s timing limits. Do not treat dormant or drought-stressed turf.

What spreader setting should I use?
Use the setting listed for your exact product and spreader, if provided. Calibrate by applying and weighing product over a measured area. Never assume another product’s setting will work.

How much nitrogen does St. Augustinegrass need?
A common warm-season maintenance range is about 2–4 pounds of actual nitrogen per 1,000 square feet per year. Soil-test results and local extension recommendations should guide the total and timing.

Can I apply weed-and-feed in hot weather?
Only if the exact label permits use under the current temperature conditions. Heat can increase turf injury risk, so do not treat when conditions exceed label limits.

Should I water after applying granular weed-and-feed?
Follow the product label. Some products require moist foliage and a rain-free period; others require watering in. Do not substitute one product’s instructions for another’s.

Can I apply it to new sod or recently planted St. Augustinegrass?
Check the label for establishment restrictions and wait periods. Do not assume a product safe for mature turf is safe for new sod.

When can people and pets return to the lawn?
Follow the label’s re-entry directions. The required interval depends on the product and its instructions.

What if I see weeds after treatment?
Wait the label’s stated response period and check its repeat-treatment interval. Do not apply another dose early or exceed the maximum rate.

What should I do if the grass turns yellow or looks damaged?
Stop further treatments, review the product and application records, and contact the manufacturer or local extension office for guidance. Do not try to correct possible herbicide injury by adding more fertilizer.

(This article was written by one of our staff writers, Victor Dempsey. Visit our Meet the Team page.)