5 Best Soil Acidifier for Yellowing St Augustine Turf

The best best soil acidifier for yellowing st augustine turf is the Ferrous Sulfate Granules 20% Iron, the only one here that pairs a 20% iron analysis with a granular form that spreads cleanly through a regular broadcast spreader. It's the smartest pick when you want to see greener blades within a couple of weeks without first testing your soil pH.

Want a slow-release, long-term pH correction instead? The Southern Ag Pelletized Soil Acidifier gets you there, as long as you understand it works over months, not days.

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This guide tells you which product actually fits your lawn's specific problem (iron chlorosis vs. high pH), which ones can burn your turf if you over-apply, and which to skip entirely if you only need a quick green-up. If your St. Augustine is yellow from a disease like take-all root rot or chinch bugs, no soil acidifier will fix that, and we cover that case in the Who Should NOT Buy section below.

Everything below comes from current Amazon product data, manufacturer specifications, and aggregate buyer feedback. We have not tested these products in a lab or in our own lawns.

Quick Answer: The Best Soil Acidifier for Yellowing St Augustine Turf

The Ferrous Sulfate Granules 20% Iron is the top pick for most homeowners with yellowing St. Augustine because it delivers fast greening with a spreader-friendly form factor. Here is the full lineup, ranked by best overall fit for this specific problem:

• Ferrous Sulfate Granules 20% Iron (Best Fast Green-Up): 20% iron analysis, granular, works in 2-3 weeks.
• Southern Ag Pelletized Soil Acidifier (Best Slow-Release pH Drop): Elemental sulfur pellets, 5 lb bag, months-long effect.
• Espoma Organic Soil Acidifier Amendment Lowers (Best Organic / Large Lawns): OMRI-listed elemental sulfur, 30 lb bag covers big areas.
• Hi-Yield (34257) Iron Plus Soil Acidifier (Best 2-in-1 Iron + N): 11-0-0 NPK plus iron, doubles as a fertilizer.
• Soil Acidifier pH Correction 90% Elemental (Best High-Concentration Sulfur): 90% elemental sulfur, 18 lb bag for serious pH correction.

Thinking about fixing a disease or a pest problem instead? Jump to Who Should NOT Buy below before you spend anything.

Comparison Table

Here's the lineup at a glance: photo, product, who it's built for, and our /10 score.

Photo	Product	Best for	Score	Buy
	Ferrous Sulfate Granules 20% Iron	Fast Green-Up for Iron Chlorosis	9.1/10	Check price →
	Southern Ag Pelletized Soil Acidifier	Slow-Release pH Drop for Lawns	8.3/10	Check price →
	Espoma Organic Soil Acidifier Amendment Lowers	Organic Lawns and Large Areas	8.5/10	Check price →
	Hi-Yield (34257) Iron Plus Soil Acidifier	2-in-1 Iron and Nitrogen Boost	7.4/10	Check price →
	Soil Acidifier pH Correction 90% Elemental	High-Concentration Sulfur for Big pH Drops	7.9/10	Check price →

Scroll sideways on small screens to see every column.

Ferrous Sulfate Granules 20% Iron: Best Fast Green-Up for Iron Chlorosis

#1

Ferrous Sulfate Granules 20% Iron

Ferrous20% Iron Granular

9.1OUT OF 10

Speed of Results9.4

Ease of Use9.3

Coverage Area8.5

Owner Verdict9.2

This is the only product in the lineup that targets the symptom (yellowing) directly, not just the cause (pH). The 20% iron analysis delivers plant-available ferrous sulfate, which is exactly the form St. Augustine grass can absorb through its blades and roots within days rather than months.

Aggregate buyer feedback shows visible greening in roughly 7-14 days on most St. Augustine lawns when applied at the label rate of about 1 lb per 1,000 sq ft. The 32 oz container covers roughly 1,000-2,000 sq ft per application depending on how heavy you set your spreader.

Flaws but not dealbreakers. It won’t permanently fix a high pH problem, just feed iron to the plant directly. Staining on concrete driveways and walkways is a real risk if you sweep granules onto hard surfaces, and overshooting the application rate can burn St. Augustine tips, which is a sensitive grass.

Need a true pH correction that lasts 6-12 months instead? The Southern Ag Pelletized Soil Acidifier further down uses elemental sulfur to actually lower soil pH over time.

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Staining: Ferrous sulfate leaves rust-colored stains on concrete, stone, and clothing. Sweep granules off hard surfaces immediately and apply when the lawn is dry to avoid tracking.

Pros

• ✓20% iron delivers visible greening in 7-14 days
• ✓Granular form works in any standard broadcast spreader
• ✓Also fixes iron chlorosis in shrubs, trees, and flowers
• ✓4.6/5 average rating across thousands of buyer reports

Cons

• ✕Does not actually lower soil pH, only feeds iron
• ✕Can stain concrete driveways and walkways rust-orange
• ✕32 oz bag may not cover large lawns (over 3,000 sq ft) in one pass

Iron Content

20%

Bag Size

32 oz

Form

Granular

Application

Broadcast spreader

Best for: Homeowners who want the fastest visible green-up on a small-to-medium St. Augustine lawn (under 3,000 sq ft) without testing soil pH first.

Check current price on Amazon →

Southern Ag Pelletized Soil Acidifier: Best Slow-Release pH Drop for Lawns

#2

Southern Ag Pelletized Soil Acidifier

SouthernPelletized Sulfur

8.3OUT OF 10

Speed of Results7.0

Ease of Use8.7

Coverage Area8.8

Owner Verdict8.7

This is the pick for homeowners who want to actually lower soil pH, not just mask yellowing. Southern Ag uses pelletized elemental sulfur, which soil bacteria convert to sulfuric acid over weeks and months, gradually dropping pH.

The 5 lb bag covers roughly 1,000-2,000 sq ft at the standard application rate for established lawns. Pellets spread cleanly through a broadcast or drop spreader without the dust and clumping issues you get with powdered sulfur.

Flaws but not dealbreakers. It takes 2-6 months to see meaningful pH change, so this is not a quick fix for an immediate yellowing crisis. Verified buyer reports note the pellets are slow to break down in cold soil below 60°F, so application timing matters.

Need faster visual results while the sulfur does its work? The Ferrous Sulfate Granules 20% Iron from pick #1 gives you visible greening in 7-14 days while you wait for pH to drop.

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Timing: Soil bacteria need soil temperatures above 60°F to convert elemental sulfur into acidifying sulfuric acid. Fall and winter applications in northern states will sit largely inactive until spring.

Pros

• ✓Actually lowers soil pH rather than just feeding iron
• ✓Pelletized form spreads cleanly with no dust
• ✓Long-lasting effect: one application can persist 6-12 months
• ✓4.4/5 average rating across hundreds of buyer reports

Cons

• ✕Takes 2-6 months to deliver visible pH change
• ✕Requires soil temps above 60°F to activate
• ✕Lower iron content than dedicated iron products

Active Ingredient

Elemental sulfur

Bag Size

5 lb

Form

Pelletized

Activation

Soil bacteria, 60°F+

Best for: Patient homeowners with confirmed high soil pH (above 7.0) who want a real long-term correction during the warm growing season.

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Espoma Organic Soil Acidifier Amendment Lowers: Best Organic Option for Large Lawns

#3

Espoma Organic Soil Acidifier Amendment Lowers

EspomaOMRI-Listed Organic

8.5OUT OF 10

Speed of Results7.2

Ease of Use8.5

Coverage Area9.4

Owner Verdict9.0

This is the OMRI-listed organic option that covers the most square footage per dollar in the lineup. Espoma’s 30 lb bag of elemental sulfur is approved for organic gardening, so it works for homeowners avoiding synthetic chemicals, and the bag size means you can treat large St. Augustine lawns in a single pass.

Manufacturer application rates suggest roughly 1.5-2 lb per 100 sq ft for established lawns needing significant pH correction, which means a 30 lb bag covers about 1,500-2,000 sq ft per application. The fine granular form works in drop or broadcast spreaders.

Flaws but not dealbreakers. Like all elemental sulfur products, it works on soil-bacteria timeline, not on plant timeline, so don’t expect visible greening for 2-4 months. The 30 lb bag is heavy to haul and store, and some buyers report the granules are finer than competitors, which means more dust during application.

Need a smaller, lighter bag for a modest lawn? The Southern Ag Pelletized Soil Acidifier in pick #2 uses the same elemental sulfur approach in a 5 lb bag that’s easier to carry.

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Storage: The 30 lb bag weighs roughly 13.6 kg. Plan for dry, covered storage because elemental sulfur clumps when it absorbs moisture, and clumps spread unevenly through a broadcast spreader.

Pros

• ✓OMRI-listed for certified organic gardening
• ✓30 lb bag covers up to 2,000 sq ft per application
• ✓Safe around kids, pets, and edibles when applied per label
• ✓4.6/5 average rating from long-term buyer feedback

Cons

• ✕Slow 2-4 month activation, no instant green-up
• ✕30 lb bag is heavy and awkward to store
• ✕Contains no iron, so it can’t fix chlorosis directly

Certification

OMRI-listed

Bag Size

30 lb

Active Ingredient

Elemental sulfur

Coverage

~2,000 sq ft / app

Best for: Organic-focused homeowners with large St. Augustine lawns (3,000+ sq ft) who want a single-bag solution and don’t need overnight results.

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Hi-Yield (34257) Iron Plus Soil Acidifier: Best 2-in-1 Iron and Nitrogen Boost

#4

Hi-Yield (34257) Iron Plus Soil Acidifier

Hi-Yield11-0-0 + Iron

7.4OUT OF 10

Speed of Results8.2

Ease of Use7.5

Coverage Area7.0

Owner Verdict6.9

This is the only product in the lineup that doubles as a fertilizer and an iron supplement, which is useful for nitrogen-deficient yellowing. Hi-Yield’s 11-0-0 analysis delivers 11% nitrogen alongside iron and acidifying compounds, so you can feed the grass and green it up in one pass.

The 3.25 lb bag is the smallest in the lineup, which makes it a fit for small lawns or spot-treating problem areas. Aggregate buyer reports show most St. Augustine lawns respond within 10-21 days, slightly slower than pure iron products but faster than elemental sulfur alone.

Flaws but not dealbreakers. The 4/5 average rating is the lowest here, and verified buyer feedback points to inconsistent granule size that causes clogging in some spreaders. The 11% nitrogen means you cannot apply it as frequently as a pure iron product without risking nitrogen burn.

Need iron without any nitrogen? The Ferrous Sulfate Granules 20% Iron at the top gives you 20% iron with zero NPK, so you control your nitrogen schedule separately.

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Nitrogen: The 11% nitrogen means this is technically a fertilizer too. Don’t apply within 6 weeks of a regular nitrogen feeding or you’ll risk burn and excessive thatch buildup on St. Augustine.

Pros

• ✓Combines 11% nitrogen with iron in one application
• ✓Small 3.25 lb bag suits lawns under 1,500 sq ft
• ✓Lower price per bag than larger competitors
• ✓Works for shrubs, trees, and acid-loving ornamentals too

Cons

• ✕4.0/5 average rating is the lowest in the lineup
• ✕Inconsistent granule size causes spreader clogging in some cases
• ✕11% nitrogen limits how often you can apply it

NPK Ratio

11-0-0

Bag Size

3.25 lb

Form

Granular

Coverage

~1,000 sq ft

Best for: Lawns that are both nitrogen-starved and iron-deficient, especially small yards where you want one product to do two jobs.

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Soil Acidifier pH Correction 90% Elemental: Best High-Concentration Sulfur for Big pH Drops

#5

Soil Acidifier pH Correction 90% Elemental

Soil90% Sulfur Concentrate

7.9OUT OF 10

Speed of Results6.8

Ease of Use7.8

Coverage Area9.2

Owner Verdict7.8

This is the highest-concentration elemental sulfur in the lineup at 90%, which matters when your soil test shows a pH above 7.5. Higher concentration means you need less product per 1,000 sq ft to achieve the same pH drop, so the 18 lb bag covers serious ground.

Manufacturer estimates put coverage around 3,000-5,000 sq ft per application depending on how aggressive a pH correction you need. The granular form is compatible with most broadcast spreaders, though the 18 lb bag is the second-heaviest in this roundup.

Flaws but not dealbreakers. The 5/5 rating is from a small sample size, so we treat it as promising but not yet proven at scale. The 90% concentration makes over-application riskier because it’s easy to swing pH too far if you miscalculate, and St. Augustine prefers pH in the 5.0-7.0 range, not below.

Need organic certification with your high-concentration sulfur? The Espoma Organic Soil Acidifier Amendment Lowers in pick #3 uses elemental sulfur too, and it’s OMRI-listed for organic gardening.

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Dosage: At 90% concentration, double-check your soil test pH and your lawn’s square footage before applying. Overshooting pH below 5.0 will damage St. Augustine stolons and turn the problem from yellowing to dieback.

Pros

• ✓90% sulfur concentration delivers stronger pH drop per pound
• ✓18 lb bag covers up to 5,000 sq ft per application
• ✓Works for blueberries, hydrangeas, and vegetable gardens too
• ✓5/5 rating from early buyer feedback (small sample)

Cons

• ✕High concentration raises risk of over-application
• ✕Limited long-term buyer track record compared to competitors
• ✕No iron content, so it can’t address chlorosis directly

Sulfur Purity

90%

Bag Size

18 lb

Form

Granular

Coverage

~3,000-5,000 sq ft

Best for: Lawns with confirmed soil pH above 7.5 where you need a strong, fast-acting elemental sulfur and you don’t mind calculating dosage carefully.

Check current price on Amazon →

Buying Guide: Active Ingredient, Iron Content, Bag Size, and Application Speed

St. Augustine grass (Stenotaphrum secundatum) is a warm-season turf that prefers soil pH between 5.0 and 7.0, with the sweet spot around 6.0-6.5. When pH climbs above 7.0, iron becomes less available to the plant, and you get interveinal chlorosis, which is the technical name for those yellow leaves with green veins.

Soil acidifiers fix this two ways: directly feeding iron, or slowly lowering pH so the soil releases more iron naturally.

Iron Supplement vs. Elemental Sulfur

The lineup splits into two camps. Pure iron products like the Ferrous Sulfate Granules 20% Iron and the Hi-Yield Iron Plus feed the plant directly. You see greening in 7-14 days, but the effect wears off as the iron is used up or leached.

Elemental sulfur products like Southern Ag, Espoma, and the 90% Soil Acidifier work through soil bacteria that take 2-6 months to convert sulfur to sulfuric acid. The trade-off is speed versus longevity.

According to Texas A&M AgriLife Extension, foliar iron applications correct chlorosis within days but don't address the underlying pH problem, which is why many extension services recommend a combined approach for high-pH soils.

Bag Size and Coverage

These five products span a wide coverage range. The smallest is the Hi-Yield 3.25 lb bag at roughly 1,000 sq ft, and the largest is the 90% Elemental Sulfur at 18 lb covering up to 5,000 sq ft. The Espoma 30 lb bag is technically the largest by weight but delivers a lower-concentration product, so its effective coverage sits around 2,000 sq ft.

Match bag size to your actual lawn square footage, not to "more is better" thinking, because elemental sulfur can damage St. Augustine if over-applied.

Form Factor: Granular vs. Pelletized

All five products in this roundup are dry granular or pelletized forms, which work in standard broadcast or drop spreaders. Granular products like Ferrous Sulfate tend to be finer and spread more evenly, while pelletized products like Southern Ag produce less dust and flow more reliably through cheaper spreaders. Either works, but if your spreader is older or has a small hopper, pellets are the lower-maintenance choice.

Who Should NOT Buy Best Soil Acidifier for Yellowing St Augustine Turf

A soil acidifier is the wrong purchase for a few specific kinds of buyers. Here's who they are, and what to look at instead.

You Suspect a Disease or Pest, Not a Nutrient Issue

If your St. Augustine has circular brown patches, thinning areas that pull up easily, or you see chinch bugs in the thatch, the yellowing is likely from take-all root rot, brown patch, or chinch bug damage. No amount of iron or sulfur will fix a fungal infection or insect infestation.

Look for a fungicide labeled for take-all patch or a curative insecticide like bifenthrin instead. The University of Florida IFAS Extension has a turfgrass disease diagnostic guide that walks through identifying these problems visually.

You Haven't Tested Your Soil pH Yet

Throwing acidifier at yellow St. Augustine without knowing your starting pH is a guessing game. If your soil pH is already below 6.0, adding more sulfur will push it into the 4.0-5.0 range, which is toxic to St.

Augustine and causes tip burn and dieback. A basic soil test kit from a local cooperative extension office costs little and tells you exactly what you need. The USDA NRCS soil testing resources can point you to regional labs that interpret results for turfgrass specifically.

You Want a One-Time Permanent Fix

Soil acidifiers don't last forever. Iron supplements wash through the soil profile in 4-8 weeks, and elemental sulfur applications typically need reapplication every 6-12 months to maintain lowered pH. If you're looking for a "fix it once and forget it" solution, you're shopping for the wrong category.

Consider replacing St. Augustine with a more alkaline-tolerant grass like zoysia or bermuda, or commit to a seasonal acidifier schedule.

Final Verdict

The Ferrous Sulfate Granules 20% Iron is the best pick for most homeowners with yellowing St. Augustine because it delivers visible results in 7-14 days, works in any standard spreader, and doesn't require a soil test to start seeing greening.

Want a true long-term pH correction instead? The Southern Ag Pelletized Soil Acidifier uses elemental sulfur to actually lower pH over 2-6 months, and the pelletized form spreads cleanly. Need a large organic-certified bag for a bigger lawn?

The Espoma Organic Soil Acidifier covers up to 2,000 sq ft per application and is OMRI-listed. Need a high-concentration sulfur for pH above 7.5? The 90% Elemental Sulfur gives you more acidifying power per pound, but watch your dosage carefully.

If your yellowing is from disease, pests, or a soil pH you haven't measured yet, skip this category and check the Who Should NOT Buy section above for what to look at instead.

FAQ

What's the best soil acidifier for yellowing St. Augustine turf overall?

The Ferrous Sulfate Granules 20% Iron is the best pick for most homeowners because the 20% iron analysis delivers visible greening in 7-14 days, and the granular form works in any standard broadcast spreader without special equipment.

How fast will I see results on my St. Augustine lawn?

Iron supplements like ferrous sulfate typically show greening in 7-14 days. Elemental sulfur products take 2-6 months because they rely on soil bacteria to convert sulfur into acidifying compounds, and that conversion is temperature-dependent below 60°F.

Can I use too much soil acidifier on St. Augustine?

Yes. St. Augustine prefers pH between 5.0 and 7.0, and pushing below 5.0 causes tip burn, stolon dieback, and can kill the grass.

Always follow label rates, and consider a soil test if your lawn is over 2,000 sq ft or has shown pH sensitivity before.

Should I water after applying soil acidifier?

For granular iron products, water lightly within 24 hours to move the iron off the blades and into the root zone. For elemental sulfur, water thoroughly to activate soil bacteria and start the conversion process. Avoid heavy irrigation that washes granules into storm drains or concrete surfaces.

Can I mix iron supplements with fertilizer?

Yes, but check your nitrogen schedule. Products like the Hi-Yield Iron Plus already contain 11% nitrogen, so applying it within 6 weeks of a regular nitrogen fertilizer can cause burn and thatch buildup on St. Augustine.

Will soil acidifier help if my grass is yellow from drought or heat stress?

No. Drought-stressed and heat-stressed St. Augustine yellows from lack of water and photosynthesis shutdown, not from iron deficiency or pH issues.

The fix is deep, infrequent watering (1-1.5 inches per week) and raising your mower blade to 3.5-4 inches during summer heat. Soil acidifiers won't help and may add unnecessary chemical load to an already stressed lawn.