A guide to Fe-EDDHSA — the chelated iron fertilizer for calcareous and high-pH soils — what it is, how it compares with EDDHA, EDTA, and iron sulfate, and how it is supplied, from a US-based distributor.
Fe-EDDHSA is a chelated iron micronutrient that keeps iron available to plants from pH 2 to 11, so it corrects iron chlorosis on calcareous and high-pH soils where iron sulfate and Fe-EDTA fail. It is applied by soil application, fertigation, and hydroponics. Stratus Chemical supplies Fe-EDDHSA 6% microgranules, with COA and SDS.
| Chemical name | Iron chelate of ethylenediamine-di(5-sulfo-2-hydroxyphenylacetic) acid |
|---|---|
| CAS number | 84539-54-8 |
| EC (EINECS) number | 283-042-4 |
| REACH name | Acetic acid, oxo-, sodium salt, reaction products with ethylenediamine and p-phenolsulphonic acid, iron sodium salts |
| Synonyms | EDDHSA-Fe, iron EDDHSA, sulfonated EDDHA iron chelate, chelated iron 6% |
| Fertilizer classification | EU PFC 1(C)(II)(a), straight inorganic micronutrient fertilizer (Regulation (EU) 2019/1009) |
| Grade supplied | 6% Fe, microgranular |
Fe-EDDHSA is iron bound to EDDHSA, a chelating agent from the EDDHA family whose aromatic rings carry sulfonate groups. The chelate wraps around the iron atom and holds it in a soluble form that plant roots can take up, while shielding it from the soil chemistry that would otherwise lock it away.
That shielding is the whole point. Iron is abundant in most soils, but above about pH 7 — and especially in calcareous soils rich in lime — it converts to insoluble oxides and hydroxides that plants cannot absorb. The crop yellows between the veins of its youngest leaves (iron chlorosis), growth slows, and yield and fruit quality fall. Fe-EDDHSA stays stable from pH 2 to 11, so it keeps delivering iron in exactly the soils where the problem occurs. The sulfonate groups also make it highly water-soluble, which suits fertigation and liquid blending.
| Appearance | Dark red-brown microgranules |
|---|---|
| Iron (Fe) chelated by EDDHSA | 6.0 ± 0.4% w/w |
| Iron (Fe) chelated by ortho-ortho EDDHSA | >3.8% w/w |
| pH (1% solution) | 7.0 ± 0.5 |
| Stability range | pH 2–11 |
| Bulk density | Approx. 600 kg/m³ |
| Potassium | Approx. 11% as K2O |
The ortho-ortho figure matters more than the total iron. In EDDHA-type chelates, the ortho-ortho isomer binds iron most tightly and stays stable at high pH; it is the fraction doing the work in calcareous soil. When comparing products, compare ortho-ortho iron, not just the headline 6%.
The primary use. Fruit trees, citrus, grapes, berries, and other sensitive crops on lime-rich or high-pH soils are treated with soil-applied Fe-EDDHSA, usually early in the season before chlorosis shows, and again as needed. Application rates depend on crop, soil, and severity and are set by the grower’s agronomist.
Fe-EDDHSA’s high solubility makes it a good fit for drip and micro-irrigation, where it can be dissolved into stock tanks and injected with the rest of the nutrient program. It stays chelated in alkaline irrigation water that would precipitate iron sulfate.
In soilless and greenhouse systems, where nutrient solutions often drift above pH 6.5, an EDDHA-type chelate keeps iron available when Fe-EDTA begins to fail.
Fertilizer blenders and formulators use Fe-EDDHSA as the iron source in water-soluble NPK and micronutrient blends, alongside zinc sulfate, copper sulfate, magnesium sulfate, and boric acid. Its roughly 11% K2O is a useful bonus in potassium-balanced formulas.
| Fe-EDDHSA | Fe-EDDHA | Fe-EDTA / Fe-DTPA | Iron sulfate | |
|---|---|---|---|---|
| Iron held available up to | pH 11 | High pH (ortho-ortho grades) | About pH 6.5 (EDTA) / 7.5 (DTPA) | Precipitates in alkaline soil |
| Calcareous soils | Effective | Effective; high ortho-ortho grades strongest | Poor | Poor |
| Water solubility | Very high | Good | High | High |
| Best fit | Fertigation, liquid blends, high pH | Soil application on severe calcareous sites | Foliar, acidic to neutral media | Acidic soils, low-cost correction |
| Relative cost | Higher | Higher | Moderate | Low |
How to choose: soil and water pH decide it. On acidic to neutral soils, iron sulfate or Fe-EDTA is cheaper and usually adequate. Above about pH 7, and especially on calcareous ground, only EDDHA-type chelates keep iron available for long. Between the two, Fe-EDDHSA’s sulfonation gives better solubility for fertigation and liquid products, while a high ortho-ortho Fe-EDDHA is often chosen for straight soil application on the most severe calcareous sites. For foliar sprays, EDTA and DTPA chelates are generally preferred.
Keep it dry. Store the microgranules in closed original packaging in a cool, dry place. Moisture causes caking and makes metering and dissolving harder.
Protect solutions from light. Iron chelates in solution can break down under sunlight. Mix fertigation stock solutions close to the time of use and keep tanks covered.
Staining. The dark red-brown color stains concrete, skin, and clothing. Wear gloves and clean spills promptly.
Fe-EDDHSA is registered under EU REACH, and EDDHSA is an authorized chelating agent under Spanish fertilizer regulation (RD 999/2017). COA and SDS are provided with every shipment.
Fe-EDDHSA is a chelated iron fertilizer used to prevent and correct iron chlorosis, the yellowing of young leaves caused by iron deficiency. It is applied through soil application, fertigation, and hydroponic systems on fruit trees, citrus, vines, vegetables, turf, and ornamentals, especially on calcareous and high-pH soils. Stratus Chemical supplies Fe-EDDHSA 6% as microgranules.
The CAS number for Fe-EDDHSA (the iron chelate of ethylenediamine-di(5-sulfo-2-hydroxyphenylacetic) acid) is 84539-54-8 and its EC number is 283-042-4.
Fe-EDDHSA and Fe-EDDHA are closely related iron chelates for high-pH soils. Fe-EDDHSA carries sulfonate groups on its aromatic rings, which make it more water-soluble and well suited to fertigation and liquid blends. Fe-EDDHA has a different CAS number and, in grades with a high ortho-ortho content, is often preferred for severely calcareous soils. Both hold iron available far above the pH where EDTA chelates fail.
In EDDHA-type iron chelates, ortho-ortho describes the isomer that binds iron most tightly and stays stable at high pH. It is the fraction that keeps iron available in calcareous soils. Stratus Chemical’s Fe-EDDHSA 6% contains 6.0 ± 0.4% chelated iron, of which more than 3.8% is chelated in the ortho-ortho form.
Fe-EDDHSA is stable between pH 2 and 11, according to the manufacturer’s technical data. That range covers acidic, neutral, and strongly alkaline soils and irrigation water, which is why EDDHA-type chelates are used where iron sulfate and Fe-EDTA stop working.
On calcareous or high-pH soils, Fe-EDDHSA is far more effective than iron sulfate or Fe-EDTA because it keeps iron soluble and available to roots. Iron sulfate converts quickly to insoluble iron oxides in alkaline soil, and Fe-EDTA loses its iron above roughly pH 6.5. On acidic soils, the cheaper sources often work, and Fe-EDDHSA’s higher cost is harder to justify.
Store Fe-EDDHSA microgranules in closed original packaging in a cool, dry place, away from moisture. Prepare fertigation stock solutions close to the time of use and keep them out of direct sunlight, because iron chelates in solution can degrade under light.
Stratus Chemical supplies Fe-EDDHSA 6% as dark red-brown microgranules, with 6.0 ± 0.4% chelated iron (more than 3.8% ortho-ortho), pH 7.0 ± 0.5 in 1% solution, and about 11% potassium as K2O. It is REACH registered and classified as an EU straight micronutrient fertilizer. A COA and SDS come with every shipment. To get pricing, send Stratus Chemical the volume and delivery location through the quote form and you will receive a response within one business day.
Looking for related products? See our crop micronutrients guide, zinc sulfate, copper sulfate, and magnesium sulfate, the full product range, or request a quote.
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