High-purity ferrous sulfate heptahydrate (iron sulfate, FeSO₄·7H₂O) for correcting iron-deficiency chlorosis, supplying sulfur, and supporting pH management in alkaline soils. Ideal for lawns, trees, shrubs, ornamentals, and garden beds. Trusted by growers since 1989 — lab tested and packaged in California.
Ferrous sulfate heptahydrate (FeSO₄·7H₂O) delivers 20% soluble iron in the Fe²⁺ form, which is more quickly available to plants than ferric (Fe³⁺) sources — particularly effective when applied as a foliar spray.
Dissolves completely with no inert fillers. Apply as a soil drench or foliar spray. For fertigation use, always jar-test first and verify water pH and equipment compatibility before injecting into irrigation lines.
Foliar applications can produce a visible greening response in new growth within days. Soil applications support longer-term correction, especially where soil pH and bicarbonate conditions are also being managed.
Oxidation of Fe²⁺ releases hydrogen ions that help lower soil pH over time — a useful dual benefit in alkaline soils where pH and iron availability are both limiting. Highly buffered or calcareous soils may require repeated applications.
Supplies 20% iron and 11.5% sulfur. Sulfur is provided in sulfate form for direct plant uptake. Soil acidification depends on the oxidation chemistry after application — not sulfate alone.
Calcium carbonate conditioner is included at low levels to maintain free-flowing granule consistency during storage and application. Its effect on product performance at the amounts used is expected to be minimal.
Packaged at our FDA-registered facility in Madera, California. Each batch is independently tested for purity and heavy metal content before release.
Third-party laboratory analysis confirms iron concentration and screens for heavy metal content — documentation available on our certificates page.
Suitable for ornamentals, fruit trees, vegetables, turf, blueberries, azaleas, and iron-sensitive plants in alkaline or compacted soils. Best results where soil pH can be actively managed alongside iron applications.
Iron and sulfate are both essential plant nutrients — no synthetic organic residues. A naturally occurring mineral salt used in agriculture for over a century.
Greenway Biotech Ferrous Sulfate is sourced as a single high-purity compound. The heptahydrate crystal form is selected for maximum water solubility and bioavailability.
Crystalline iron(II) sulfate with seven water molecules. The Fe²⁺ oxidation state is the form plants absorb most readily. Provides 20% elemental iron and 11.5% sulfur. High-purity grade ensures consistent analysis and minimal impurities.
Food-grade conditioner included at low levels to maintain free-flowing granule consistency during storage and application. Its effect on iron availability and soil pH at the amounts used is expected to be minimal.
Cofactor in chlorophyll synthesis, electron transport chains (ferredoxin), and over 100 enzymatic reactions. Iron deficiency blocks chlorophyll formation, causing interveinal chlorosis on young leaves. Fe²⁺ is the ionic form absorbed at the root surface; Fe³⁺ must first be reduced before uptake can occur.
Component of cysteine, methionine, and glutathione. Provided in sulfate form for direct plant uptake. Soil acidification after ferrous sulfate application depends on oxidation and hydrolysis chemistry — not the presence of sulfate alone.
Most iron in soil exists as insoluble Fe³⁺ (ferric) compounds, especially above pH 6.5. Plants must first reduce Fe³⁺ to Fe²⁺ at the root surface before uptake can occur. Ferrous sulfate supplies iron in a readily soluble form that helps correct deficiency quickly — particularly as a foliar spray. In alkaline soils, dissolved Fe²⁺ can re-oxidize relatively quickly, so repeated applications or chelated iron may provide more durable results depending on soil conditions.
Iron is the fourth most abundant element in the Earth's crust, yet deficiency is widespread in soils with pH above 7.0. At high pH, Fe²⁺ rapidly oxidizes to insoluble Fe(OH)₃. High-bicarbonate irrigation water further raises root zone pH and can contribute to recurring chlorosis even after treatment — addressing water alkalinity is often part of a complete management program.
When ferrous sulfate is applied to soil, it undergoes oxidation: 4FeSO₄ + O₂ + 10H₂O → 4Fe(OH)₃ + 4H₂SO₄. The sulfuric acid produced releases H⁺ ions, helping lower soil pH over time. The reaction rate depends on soil moisture, temperature, and microbial activity, making ferrous sulfate a generally faster-acting acidifier than elemental sulfur, which requires bacterial oxidation and is slower in cool or compacted soils. In strongly calcareous soils, ferrous sulfate alone may not produce durable pH reduction without repeated seasonal applications.
Iron deficiency presents as interveinal chlorosis — yellow tissue between green veins — beginning on the youngest leaves. Confirm deficiency before applying; excess iron can compete with manganese and zinc uptake.
| Plant Type | Rate per 100 sq ft | Approx. Measure |
|---|---|---|
| Flowers & Vegetables | ¼–½ lb | ½–1 cup |
| Trees & Shrubs | ½–1 lb | 1–2 cups |
| Large Trees | ½ cup per inch trunk diameter | Apply under drip line |
| Deficiency Level | Rate | Frequency |
|---|---|---|
| Preventive | 0.5–1 tbsp/gallon | Monthly |
| Mild | 1 tbsp/gallon | Every 2–3 weeks |
| Moderate | 1–1.5 tbsp/gallon | Every 2 weeks |
| Severe | 1.5 tbsp/gallon — repeat after observing plant response | Weekly until corrected |
| Current pH | Target pH | Sandy Soil | Loam Soil | Clay Soil |
|---|---|---|---|---|
| 8.5 | 6.5–6.8 | 230 lbs | 285 lbs | 345 lbs |
| 8.0 | 6.5–6.8 | 140 lbs | 170 lbs | 230 lbs |
| 7.5 | 6.5–6.8 | 55 lbs | 90 lbs | 115 lbs |
| 7.0 | 6.5–6.8 | 10 lbs | 20 lbs | 35 lbs |
| Use | Rate | Method |
|---|---|---|
| Lawn Moss Management | 5 lbs/1,000 sq ft | Broadcast dry; follow all label directions |
| Structure Moss (roofs, walks) | 3 oz/gallon water | Spray; rinse after 24 hrs to prevent staining |
| Hydroponics (with caution) | Use only in carefully controlled formulations | Not preferred for recirculating systems — chelated iron sources are more suitable for most crops. Monitor EC closely if used. |
When plants show severe interveinal chlorosis (leaves nearly white), a foliar spray provides a rapid cosmetic response while a simultaneous soil application helps address the underlying pH condition. Apply foliar first for the quick visual improvement, then broadcast soil product and water in. For best long-term results, also address irrigation water alkalinity if bicarbonate levels are high.
Refer to the Safety Data Sheet (SDS) for complete safety information.
EDTA-chelated iron stays plant-available across a wider pH range. Ideal for mixed plantings where soil pH cannot be easily lowered.
DTPA chelate is one of the most reliable choices for hydroponic and soilless systems. Remains stable in nutrient solution up to pH 7.0.
Manganese deficiency presents similarly to iron chlorosis. Correct both when symptoms are ambiguous or when pH is above 7.5.
Zinc availability also declines at high pH. Often deficient alongside iron in alkaline, calcareous soils.
Among the most acidifying nitrogen sources available. Pairs with ferrous sulfate for a sustained, multi-season pH reduction program in alkaline soils.
Improves soil structure in sodic or compacted soils without significantly changing pH — a good complement when structure, not pH, is the limiting factor.
| Factor | Ferrous Sulfate 20% Fe | Chelated Iron EDTA 13% | Chelated Iron DTPA 11% |
|---|---|---|---|
| Best soil pH range | Below 7.0 | Up to pH 6.5 | Up to pH 7.0 |
| Soil application | ✅ Yes | ✅ Yes | ✅ Yes |
| Foliar application | ✅ Yes (with care) | ✅ Yes | ✅ Yes |
| Hydroponics | ⚠️ Not preferred | ⚠️ Stable to pH 6.5 | ✅ Preferred (stable to pH 7.0) |
| Soil pH support | ✅ Yes — acidifying | ❌ No pH effect | ❌ No pH effect |
| Moss management | ✅ Yes (label use) | ❌ No | ❌ No |
| Relative cost | Lowest | Higher | Higher |
Iron chlorosis occurs when plants cannot access sufficient Fe²⁺ for chlorophyll synthesis, producing the characteristic yellow tissue between green veins on young leaves. The most common cause is not a lack of iron in the soil — it is high soil pH (above 7.0) that converts soluble Fe²⁺ into insoluble Fe(OH)₃ that roots cannot absorb. Other contributing factors include waterlogged soils, high phosphorus levels, and soils high in bicarbonate from irrigation water. Ferrous sulfate corrects both the iron deficiency and the underlying pH condition. For a deeper look at how iron functions in plant growth, see What Are the Effects of Iron on Plant Growth?
Foliar applications typically show a visible greening response in new growth within 5–10 days as iron becomes available directly through the leaf surface. Existing chlorotic leaves will not fully green back — improvement is most obvious in the new growth that emerges after treatment. Soil applications work more gradually, acidifying the root zone over 2–6 weeks as the product oxidizes and reacts with soil minerals. For severe or persistent chlorosis, combining a foliar spray for immediate response with a soil application for long-term correction gives the best outcome.
Yes — this is one of the most important handling precautions. Ferrous sulfate causes rust-brown stains on concrete, stone, brick, pavers, and painted surfaces that are very difficult to remove once the iron oxidizes and sets into the material. Always sweep dry granules off hardscape immediately after application before watering. Rinse foliar spray off sidewalks and driveways right away. If staining does occur, oxalic acid-based rust removers can reduce (though rarely eliminate) discoloration.
Ferrous sulfate is not recommended for hydroponic or soilless nutrient solutions. Fe²⁺ is unstable in solution and rapidly oxidizes to Fe³⁺ (insoluble) at pH levels above 5.5–6.0, precipitating out of solution. For hydroponic and container applications, Chelated Iron DTPA 11% (stable to pH 7.0) or Chelated Iron EDTA 13% (stable to pH 6.5) are more suitable choices. For more on choosing between sulfate and chelated iron, see Sulfate vs. Chelated Fertilizers: Key Differences.
Ferrous sulfate is commonly used as part of lawn moss management programs — iron at the rates used for moss control is toxic to moss cells at concentrations that established turfgrass can generally tolerate. At 5 lbs per 1,000 sq ft, moss typically turns black within 7–10 days. After it turns black, rake it out thoroughly before overseeding bare areas. For lasting results, address the underlying conditions that favor moss — shade, compaction, poor drainage, and low soil pH. Follow all label directions. For more tips on long-term moss management, see The Real Reason Why Moss Keeps Growing in Your Garden.
Once watered in and dry, ferrous sulfate at normal fertilizer rates poses minimal risk to pets walking on treated areas. However, direct ingestion of dry product can cause gastrointestinal upset in dogs and cats — keep pets off treated areas until the product has been thoroughly watered in and the soil surface is dry. Do not allow product to wash into water features or natural ponds where fish are present, as iron toxicity can affect aquatic life at elevated concentrations.
Ferrous sulfate supplies iron as the free Fe²⁺ ion — effective and economical in acid to neutral soils (pH below 6.5–7.0), but rapidly converts to insoluble Fe³⁺ in alkaline conditions. Chelated iron (EDTA or DTPA) binds iron inside an organic molecule that protects it from reacting with soil pH, keeping it plant-available across a broader pH range. For most alkaline garden soils, starting with ferrous sulfate and monitoring pH response is a practical first approach. For a full comparison, see Sulfate vs. Chelated Fertilizers: Key Differences and Garden Benefits.
We stand behind every product with a 90-day money-back guarantee. If you are not completely satisfied, return the unused portion in its original packaging and we will process a full refund. See our Returns & Shipping page for complete details.
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Greenway Biotech, Inc. has been formulating and distributing high-quality fertilizers and plant nutrition products since 1989 — over 35 years serving commercial growers and home gardeners across the United States. Based in Madera, California, our products are packaged at our FDA-registered facility and backed by independent third-party testing. We are committed to technical accuracy, regulatory compliance, and practical products that work.
Learn how to diagnose iron deficiency, compare iron sources, and build a longer-term chlorosis correction plan.
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