Iron chlorosis is the yellowing of young leaves, with the veins still green, that appears when the plant cannot take up iron or move it to the new leaf. In calcareous soils the iron is in the soil, but the high pH and the bicarbonates leave it in forms the root does not take up. No organism causes it: it is a nutritional deficiency, and it is tackled on two fronts at once, the management of the soil and of the irrigation water and an iron corrector applied to the leaf or through the irrigation. Diagnosis is confirmed by leaf analysis and technical advice.
How to recognise iron chlorosis: young leaf, yellow between the veins
What you see
Iron chlorosis begins on the new shoots. Iron moves poorly within the plant: the old leaf keeps what it received and the young leaf emerges without it. The leaf blade loses its green between the veins, which stay green and draw a fine network over the yellow background. If the deficiency continues, the yellow turns almost white, the leaf comes out smaller and ends up drying at the edges. “Yellow leaves with green veins” is exactly the picture.
What it is confused with
A yellow leaf has several causes and three of them resemble iron chlorosis. Two questions tell them apart: is the affected leaf young or old? Does the vein stay green or does it turn yellow with the rest?
| What you see | Where | Probable cause |
|---|---|---|
| Yellow blade, fine green veins | Young leaves, new shoots | Iron deficiency (iron chlorosis) |
| Uniform yellow, vein included | Old leaves first | Nitrogen deficiency |
| Yellow between the veins, broad green vein | Old leaves, base of the shoot | Magnesium deficiency |
| General yellowing, drooping leaf, dark root | Whole plant, with no pattern by age | Waterlogging or root damage |
It is a field key, not a diagnosis: it serves to decide what to analyse.
How it is confirmed
By leaf analysis. Our data sheets repeat it: the deficiency is confirmed “according to leaf and soil analysis” and the product is used “under technical advice”. Before applying iron it is worth knowing that what is missing is iron. The thresholds used to interpret the analysis are set by whoever carries it out: we do not publish them here.
Why it happens in calcareous soil even though there is iron
Calcareous soil has iron to spare; what fails is the form. At high pH, iron passes into poorly soluble forms that the root cannot take up, and the active lime, the fine fraction of carbonate that reacts with the soil water, keeps that pH high season after season. The bicarbonates in the irrigation water do the same from outside: that is why iron chlorosis sometimes appears in plots that did not show it before, when the water changes.
Two management factors worsen the picture. Waterlogging and compaction leave the root without air, and it needs oxygen to reduce iron and absorb it. And the antagonisms: excesses of phosphorus, manganese, zinc or copper compete with iron at the root and within the plant. Spring cold, which slows the root just when the new flush calls for iron, explains why the symptom is usually strongest on the first leaves of the year. We do not give figures for pH or active lime: that figure belongs to the soil analysis of each plot.
Crops that suffer from iron chlorosis
The most sensitive are fruit trees grafted on rootstocks that take up iron poorly in calcareous soil and acid-soil crops planted in alkaline soil. The table says where it shows first and whether our HIERRO data sheet publishes doses for their group.
| Crop | Where it appears first | Dose in the HIERRO data sheet? |
|---|---|---|
| Citrus (lemon, orange, mandarin) | Spring flush; lemon is the most sensitive | Yes: “fruit trees” |
| Olive | Current-year shoots in very calcareous soils; less frequent than in citrus | Yes: “fruit trees” |
| Vine | Young shoots; depends on the rootstock | Yes: “fruit trees” |
| Almond and pistachio | New shoots, especially in hedge plantings | Yes: “fruit trees” |
| Apple and pear | Current-year shoots; pear is the most sensitive | Yes: “fruit trees” |
| Blueberry | Whole plant: an acid-soil crop | Yes: “fruit trees” |
| Avocado and mango | New leaves of each flush | Yes: “fruit trees” |
| Vegetable crops (tomato, pepper, cucumber, melon…) | Leaves at the tip, especially with bicarbonate-rich water | Yes: “vegetable crops” |
| Arable crops (maize, sunflower, sugar beet…) | Young leaves in patches, over the lime spots | Yes: “arable crops” |
A crop appearing in the data sheet means that we publish doses and timing for its group; the sensitivity of each species and rootstock is general agronomic knowledge and carries no figure here.
What management does before the corrector
The corrector attends to this season’s leaf; management attends to the cause, slowly and with no fixed deadline. Five levers are in the hands of the grower:
- Organic matter. A soil with more organic matter holds iron in forms the root takes up better and has more air. In our catalogue, the humic extract input by fertigation is HUMIC FULVIC+ALGAS, which the data sheet places “at any stage of the growing cycle”. We publish no data linking that product to iron chlorosis: it is a humic and fulvic acid input, not an iron corrector.
- Irrigation without waterlogging. Shorter, more frequent irrigations in heavy soils. A root without air does not take up iron even when it is right in front of it.
- Irrigation water. A water analysis says how much bicarbonate comes in with each irrigation; acidifying it is common practice when levels are high, and the decision rests with the farm’s technical adviser.
- Rootstock. In citrus, vine and pome fruit, lime tolerance is decided at planting. It is the lever that weighs most and the only one that cannot be moved in an established planting.
- Do not add antagonists. Do not mix iron with phosphates (“do not mix with phosphate products”, says our data sheet) and do not over-fertilise with phosphorus or other micronutrients in a plot that already shows iron chlorosis.
What an iron corrector does in organic farming
An iron corrector supplies iron in a form the plant can take up through the leaf or through the root. It does not change the soil or the water: it puts the nutrient where the plant needs it, in the current season. That is why it goes alongside management, not in its place.
What our iron corrector contains
The FENORGANIC HIERRO data sheet declares three composition lines: “Total iron (Fe) — 6.50% w/w · 7.67% w/v”, “Total iron oxide (FeO) — 8.38% w/w · 9.89% w/v” and “Single-cell freshwater algae solution — 25.00% w/w · 29.50% w/v”. It is a “liquid, brown” and is measured in litres. The two iron figures are the same quantity expressed in two ways (the oxide counts the oxygen), and how to read that pair is explained in how to read a fertiliser technical data sheet.
Through the leaf or through the irrigation
The foliar route takes iron to the leaf that has already emerged without passing through the soil that blocks it. Fertigation takes it to the root, where the blockage is, and feeds the subsequent flushes. Our data sheet publishes both routes for three crop groups:
| Crop group | Foliar | Fertigation |
|---|---|---|
| Fruit trees (olive, almond, pistachio, vine, citrus, apple, pear, blueberry, avocado, mango) | 2-3 L/1,000 L per application; severe deficiency: up to 3 applications | 2-3 L/ha per application |
| Vegetable crops (tomato, potato, cucumber, melon, courgette, cauliflower, onion, carrot, pepper) | 3-4 L/1,000 L per application; severe deficiency: up to 4 applications | 3-4 L/ha per application |
| Arable crops (cereals, lucerne, cotton, sugar beet, maize, sunflower) | 4-6 L/1,000 L per application; severe deficiency: up to 4 applications | 4-6 L/ha per application; maximum 6 L/ha split, at 10-15 day intervals |
By the foliar route the dose is per volume of spray mix (litres of product per thousand litres of water); by fertigation, per area. When each route is advisable, at what time of day, humidity and temperature, is covered in foliar fertiliser or fertigation. “Maintenance” is the base dose and “severe deficiency” the regime with a confirmed deficiency: what changes is the number of applications.
When and how to prepare it
The data sheet places the timing in the “vegetative stage, post-flowering and stages of highest vegetative activity (fruit set, ripening, etc.)”, that is, when there is new leaf calling for it, with the cadence “generally in weekly applications: between 2 and 4 applications depending on the crop”. In fertigation, the rule is “split the input (max. 6 L/ha) at 10-15 day intervals”. The first foliar application is made when the spring flush already has developed leaf: that is when the symptom is visible and when the leaf can absorb.
Two instructions from the data sheet before opening the container: “pre-dilute before pouring into the irrigation or spray tank; shake the container vigorously before use”. And a warning about its appearance: “physical characteristics and appearance may vary owing to the organic nature of the product”.
What the data sheet declares and what it does not
Anyone searching for “organic iron chelate” will find correctors on the market that declare the agent keeping the iron in solution. Our data sheet declares total iron, iron oxide and single-cell freshwater algae solution; it declares no chelating agent, and that is why we do not call our product a chelate.
On suitability for organic farming: FENORGANIC HIERRO is a “product suitable for use in organic farming” and is listed in the annex of the ECOCERT S.A.S input attestation No. 245895/29/290920251037 (“EU - Inputs Attestation” programme, Regulations (EU) 2018/848 and 2021/1165), valid until 31 March 2027. It is not listed in the annex of the USDA NOP programme. The full document is in the input attestations and the procedure for checking any input is in how to check suitability for organic farming.
On the response: we publish no figures or timescales. “How long it takes to show” depends on the crop, the route and the degree of deficiency; it is checked with the season’s leaf analysis, not with a catalogue figure.
And on micronutrient mixes: FENORGANIC MICROELEMENTOS declares “Iron (Fe) — 0.20% w/w · 0.24% w/v” alongside “Zinc (Zn) — 1.50% w/w” and “Manganese (Mn) — 0.75% w/w”. It is a maintenance input of several micronutrients, not an iron corrector.
What not to mix
The HIERRO data sheet speaks in both directions: “being completely neutral, this fertiliser is safe and compatible with other agricultural treatments”, and a single incompatibility, “do not mix with phosphate products”, because phosphorus and iron form insoluble compounds in the tank and in the soil. We publish no mixing order or spray-mix pH with a number: the data sheet does not give one.
Frequently asked questions
What is iron chlorosis in citrus and why is it so frequent in lemon?
It is the yellowing of the new leaf with green veins due to a lack of available iron. Citrus is mostly grown on calcareous soil and with bicarbonate-rich water, and lemon is the one that takes up iron worst under those conditions. Our HIERRO data sheet publishes doses for citrus in the fruit trees group.
Yellow leaves with green veins: lack of water or lack of iron?
If the yellow is on the young leaves and the vein stays green, iron is the likely cause. Lack of water dries and curls the leaf without that pattern; excess water yellows it entirely and with no pattern by age. Confirmation is the leaf analysis, not the eye.
Is iron chlorosis in olive treated the same way?
Yes, in essentials: the same symptom on the current-year shoot, the same cause in calcareous soil and the same data sheet, which includes olive in the fruit trees group. HIERRO is not part of the tank mixes of the olive grove fertilisation programme, which is a maintenance programme, not a deficiency-correction programme.
Is there an organic iron chelate?
What has to be looked at is the annex of the product’s input attestation, not its trade name. An iron corrector may be suitable for use in organic farming whether or not it declares a chelating agent. Ours is listed in the EU annex and declares no chelating agent, and we say so in the data sheet.
Foliar or fertigation for iron chlorosis?
Foliar when there is developed leaf to attend to in the season: the iron does not pass through the soil. Fertigation when the blockage is at the root and the aim is to feed the subsequent flushes. In a confirmed deficiency they are combined, each with its dose from the data sheet.
The 26 data sheets, with their doses by route and crop group, are in the full catalogue; the correctors, in correctors and nutrients. If you have a yellow leaf in front of you and do not know whether it is iron, the technical enquiry exists for that: we reply with the data sheet and, if need be, with a leaf analysis along the way.