Organic Ferrous Sulfate (Iron Sulfate) | 20% Iron (Fe)
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- $ 19.99
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- $ 19.99
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Ferrous Sulfate Fertilizer (20% Iron)
Pure ferrous sulfate heptahydrate (FeSO₄·7H₂O) with 20% elemental iron — corrects iron-deficiency chlorosis fast. 100% water-soluble for soil drench, foliar spray, or pH adjustment. Professional-grade, independently lab tested.
Ideal Applications
FEATURES
🔬 20% Elemental Iron
Ferrous sulfate heptahydrate (FeSO₄·7H₂O) delivers 20% Fe²⁺ — the plant-available form that corrects iron chlorosis faster than ferric (Fe³⁺) sources.
⚡ 100% Water Soluble
Dissolves completely with no inert fillers. Apply as a soil drench, foliar spray, or inject directly into irrigation lines for immediate iron delivery.
🌿 Corrects Chlorosis Fast
Interveinal yellowing on young leaves responds to foliar applications within days. Soil applications provide sustained correction over weeks.
📊 Acidifies Alkaline Soils
Oxidation of Fe²⁺ releases hydrogen ions that lower soil pH — a dual benefit where iron fertilization also improves availability of other pH-sensitive nutrients.
🏠 Multi-Purpose Formula
Registered for use in gardens, lawns, ponds (algae control), moss removal on structures, animal feed supplementation, and water treatment applications.
🛡️ Anti-Caking Technology
Calcium carbonate conditioner prevents clumping in storage, ensuring consistent granule flow and accurate calibration when applied through spreaders.
🇺🇸 Packaged in California
Packaged at our FDA-registered facility in Madera, California. Each batch is independently tested for purity and heavy metal content before release.
🧪 Independently Lab Tested
Third-party laboratory analysis confirms iron concentration and screens for heavy metal content — documentation available on request.
🌾 Broad Crop Compatibility
Suitable for ornamentals, fruit trees, vegetables, turf, blueberries, azaleas, and any iron-sensitive crop or landscape planting in alkaline or compacted soils.
♻️ Minimal Residue
Iron and sulfate are both essential plant nutrients — no synthetic organic residues. Sulfate byproduct further contributes to soil pH management and sulfur nutrition.
DERIVED FROM
Greenway Biotech Ferrous Sulfate is sourced as a single high-purity compound. The heptahydrate crystal form is selected for maximum water solubility and bioavailability.
Iron Source
Ferrous Sulfate Heptahydrate (FeSO₄·7H₂O)
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.
Flow Agent
Calcium Carbonate (CaCO₃)
Food-grade anti-caking agent added at low levels to maintain free-flowing granule consistency during storage and application. Does not affect iron availability or soil pH calculations.
SCIENCE BEHIND THE FORMULA
Fe — Iron (20%)
Cofactor in chlorophyll synthesis, electron transport chains (ferredoxin), and over 100 enzymatic reactions. Iron deficiency blocks chlorophyll formation, causing interveinal chlorosis on young leaves.
S — Sulfur (11.5%)
Component of cysteine, methionine, and glutathione. Also participates in soil acidification: Fe²⁺ oxidation produces sulfuric acid (H₂SO₄), releasing H⁺ ions that lower soil pH around the root zone.
Why Fe²⁺ (Ferrous) Over Fe³⁺ (Ferric)?
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 already in the Fe²⁺ state, bypassing this reduction step and making it immediately available — particularly important in alkaline soils where reduction capacity is limited.
Why Iron Deficiency Is Common in Western Soils
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. Bicarbonate in irrigation water further raises root zone pH. Ferrous sulfate addresses both the deficiency and the underlying pH condition simultaneously.
Soil pH Mechanism
When ferrous sulfate is applied to soil, it undergoes oxidation: 4FeSO₄ + O₂ + 8H₂O → 4Fe(OH)₃ + 4H₂SO₄. The sulfuric acid produced releases H⁺ ions, lowering soil pH. The reaction rate depends on soil moisture, temperature, and microbial activity, making ferrous sulfate a faster-acting acidifier than elemental sulfur.
APPLICATION RATES & DIRECTIONS
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.
Garden & Landscape (Soil Application)
| 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 |
Foliar Spray
| Deficiency Level | Rate | Frequency |
|---|---|---|
| Preventive | 1 tbsp/gallon | Monthly |
| Mild | 1–1.5 tbsp/gallon | Every 2–3 weeks |
| Moderate | 2 tbsp/gallon | Every 2 weeks |
| Severe | 2–3 tbsp/gallon | Weekly until corrected |
Soil pH Adjustment (per 1,000 sq ft)
| 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 |
Specialty Applications
| Use | Rate | Method |
|---|---|---|
| Lawn Moss Control | 5 lbs/1,000 sq ft | Broadcast dry |
| Structure Moss (roofs, walks) | 3 oz/gallon water | Spray; rinse after 24 hrs |
| Pond Algae Control | Per system volume | Professional use |
| Animal Feed Additive | Per feed specification | Mix into feed |
HOW TO USE
Foliar Spray (Fastest Results)
- Dissolve 1–2 tbsp of ferrous sulfate per 1 gallon of water. Use warm water for faster dissolution.
- Fill a clean sprayer and apply to foliage until leaves are evenly wet but not dripping.
- Spray in the early morning or evening — avoid midday heat to prevent leaf scorch.
- Repeat every 1–2 weeks until new growth shows healthy green color.
- Do not spray within 48 hours of a fertilizer application high in phosphorus, as phosphorus can interfere with iron uptake.
Soil Application
- Measure the treatment area in square feet and calculate required amount from the Application Rates table.
- Broadcast granules evenly over the soil surface or work into the top 2–3 inches.
- Water thoroughly after application to begin dissolving and moving iron into the root zone.
- For trees, apply under the drip line — not against the trunk — at ½ cup per inch of trunk diameter.
- Sweep any granules off concrete, brick, or stone surfaces immediately to prevent staining.
Moss Control
- For lawns, broadcast 5 lbs per 1,000 sq ft dry. Moss turns black within 7–10 days; rake out dead moss before reseeding.
- For roofs and structures, dissolve 3 oz per gallon and spray. Allow 24 hours of contact time, then rinse thoroughly to prevent surface staining.
pH Adjustment
- Test current soil pH with a reliable meter or test kit before applying.
- Use the pH Adjustment table to determine correct rate for your soil type and starting pH.
- Broadcast evenly and water in. Re-test pH after 4–6 weeks before applying additional product.
- Work in stages for large pH drops — do not attempt to change pH more than 0.5–1.0 units per application.
Pro Tip: Combine Foliar + Soil for Severe Chlorosis
When plants show severe interveinal chlorosis (leaves nearly white), foliar spray provides immediate color response while a simultaneous soil application corrects the underlying pH problem. Apply foliar first for the quick visual improvement, then broadcast soil product and water in. This two-pronged approach typically resolves chronic chlorosis in alkaline soils within 2–3 weeks.
When Ferrous Sulfate Is the Right Choice
- Soil pH is above 7.0 and plants show interveinal chlorosis on new growth
- You need a fast-acting iron source for immediate foliar correction
- You want to acidify soil while simultaneously supplying iron
- Moss control is needed on lawns or hardscaping
- Acid-loving plants (blueberries, azaleas, gardenias, camellias) are struggling in alkaline conditions
When to Consider Other Options
- Soil pH is already below 6.5 — iron deficiency at low pH may indicate a different nutrient interaction; consider Chelated Iron EDTA 13% for better stability across pH ranges
- Hydroponic or soilless systems — use Chelated Iron DTPA 11% for pH-stable iron in nutrient solution
- Symptoms appear on older leaves first — this pattern suggests a different deficiency (manganese or nitrogen), not iron
FERROUS SULFATE CALCULATOR
SAFETY & HANDLING
Personal Protective Equipment (PPE)
- Wear gloves when handling dry product — ferrous sulfate can stain skin and cause mild irritation with prolonged contact
- Wear safety glasses when mixing concentrated solutions or applying as a spray
- Consider a dust mask (N95) when handling in windy conditions to avoid inhalation of fine powder
- Wear old or protective clothing — ferrous sulfate causes permanent rust-colored stains on fabric
Storage Guidelines
- Store in a cool, dry location away from heat sources and direct sunlight
- Keep in the original sealed bag or transfer to an airtight container — ferrous sulfate is hygroscopic and will absorb moisture and cake if exposed to humid air
- Store away from alkaline materials (lime, wood ash) which can neutralize the product
- Keep out of reach of children and pets
- Do not store in metal containers — ferrous sulfate is corrosive to iron and steel
Application Precautions
- Staining risk: Keep product away from concrete, stone, brick, siding, and light-colored surfaces. Stains are very difficult to remove once dry
- Do not over-apply: Excessive iron can antagonize manganese and zinc uptake. Always apply based on measured deficiency, not as a general preventive at high rates
- Protect nearby plants: At moss-control rates (5 lbs/1,000 sq ft), the product will also temporarily discolor and stress turfgrass — this is normal and recovery occurs within 2–3 weeks
- Water bodies: Do not allow product to wash into natural waterways, ponds, or storm drains at landscape rates
- Not for use in true hydroponics — use chelated iron forms for soilless systems
First Aid
- Eye contact: Flush immediately with clean water for 15 minutes, holding eyelids open. Seek medical attention if irritation persists
- Skin contact: Rinse thoroughly with soap and water. Remove stained clothing. Seek medical attention if irritation develops
- Ingestion: Do not induce vomiting. Rinse mouth with water and drink 1–2 glasses of water. Contact Poison Control (1-800-222-1222) or seek medical attention immediately
- Inhalation: Move to fresh air. If breathing difficulty persists, seek medical attention
Refer to the Safety Data Sheet (SDS) for complete safety information.
COMPLETE YOUR SYSTEM
Chelated Iron — pH-Stable Alternatives
Chelated Iron EDTA 13%
EDTA-chelated iron stays plant-available across a wider pH range. Ideal for mixed plantings where soil pH cannot be easily lowered.
Chelated Iron DTPA 11%
DTPA chelate is the standard for hydroponic and soilless systems. Remains stable in nutrient solution up to pH 7.0.
Complementary Micronutrients
Chelated Manganese EDTA
Manganese deficiency presents similarly to iron chlorosis. Correct both when symptoms are ambiguous or when pH is above 7.5.
Chelated Zinc EDTA
Zinc availability also declines at high pH. Often deficient alongside iron in alkaline, calcareous soils.
Soil Acidification Support
Ammonium Sulfate 21-0-0
The most acidifying nitrogen source available. Pairs with ferrous sulfate for a sustained, multi-season pH reduction program in alkaline soils.
Gypsum (Calcium Sulfate)
Improves soil structure in sodic or compacted soils without significantly changing pH — a good complement when structure, not pH, is the limiting factor.
FREQUENTLY ASKED QUESTIONS
What causes iron deficiency chlorosis in plants?
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.
How quickly will ferrous sulfate correct yellowing leaves?
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.
Will ferrous sulfate stain my driveway or patio?
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.
Can I use ferrous sulfate in hydroponics or container systems?
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 and clogging emitters. For hydroponic and container applications, use Chelated Iron DTPA 11% (stable to pH 7.0) or Chelated Iron EDTA 13% (stable to pH 6.5).
How does ferrous sulfate control moss?
Ferrous sulfate kills moss through desiccation and disruption of photosynthesis — iron ions are toxic to moss cells at concentrations that turfgrass tolerates. At 5 lbs per 1,000 sq ft on lawns, moss turns black and dies within 7–10 days. After the dead moss turns black, rake it out thoroughly before overseeding bare areas. For more tips on long-term moss management, see The Real Reason Why Moss Keeps Growing in Your Garden.
Is ferrous sulfate safe around pets and wildlife?
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.
What is the difference between ferrous sulfate and chelated iron?
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.
GROW WITH CONFIDENCE
Quality & Purity Standards
- High-purity ferrous sulfate heptahydrate with confirmed 20% elemental iron analysis
- Independently tested by third-party laboratory for iron concentration and heavy metal content
- Packaged at our FDA-registered facility in Madera, California
- Calcium carbonate anti-caking agent ensures consistent flow and accurate application
- Every batch tested for heavy metals — documentation available on request
Returns & Guarantee
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.
Sustainability
- Precision dosing guidance reduces over-application and nutrient runoff
- Resealable packaging extends product shelf life and reduces waste
- Iron and sulfate are naturally occurring mineral nutrients with no synthetic organic residues
- Supporting soil health through pH management reduces long-term fertilizer dependency
Charitable Contributions
1% of all profits support our foundation focused on improving educational opportunities for children. Learn more at greenway.foundation.
About Greenway Biotech, Inc.
Greenway Biotech, Inc. has been formulating and distributing high-quality fertilizers and plant nutrition products since 1989. Based in Madera, California, we serve commercial growers and home gardeners throughout the San Joaquin Valley and across the United States. 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.
DOCUMENTS
- 📄 Safety Data Sheet (SDS)
- 📋 Product Label — Coming Soon
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