Foliar fertiliser or fertigation: when the leaf absorbs and when irrigation is the better choice

Foliar fertiliser or fertigation: a foliar fertiliser corrects quickly and in small quantities, because the nutrient enters through the leaf; fertigation feeds the crop through the root with the irrigation water, in larger quantities and continuously. One route serves to correct and the other to feed, and neither replaces base fertilisation: foliar feeding complements it. This guide says when the leaf absorbs, what is corrected well through it and when irrigation is the better choice, with the doses our data sheets publish.

Foliar and root fertilisers: what each route does and what it does not

A fertiliser reaches the plant by two paths. By the foliar route it is sprayed diluted onto the leaf and enters through the cuticle and the stomata; by the root route (soil application or fertigation) it is incorporated into the soil or the irrigation water and the root takes it up. What changes is not the product, which is often the same, but the quantity each route admits, the speed at which it acts and what it takes for it to work.

The debate over foliar feeding exists and we acknowledge it: no foliar fertiliser covers the total requirements of a crop in production, because the leaf does not admit the nitrogen, phosphorus and potassium that a crop extracts over a season. What foliar feeding does well is correct a specific deficiency, in a short time and without depending on what happens in the soil. With that boundary clear, choosing the route is no longer a matter of opinion.

When to apply foliar fertiliser: time of day, humidity, temperature and crop condition

For the leaf to absorb, the spray mix has to remain on it and the plant has to be active. The application conditions are part of the dose, and our data sheets write them down.

Time of day and radiation

In strong sun the spray mix evaporates before it enters and the concentration on the leaf rises: that is the path to phytotoxicity. That is why the data sheet for FÓSFORO 20 LÍQUIDO asks to “apply early in the morning or late in the evening to reduce the risk of phytotoxicity”, and the one for NITRÓGENO 16 repeats it in the same words.

Rain, drought and heat

Rain washes the spray mix off before it enters; extreme drought shuts the plant down; heat dries the droplet and concentrates what remains. The data sheet for MICROELEMENTOS asks to avoid foliar treatments in extreme drought, humidity, rain or forecast extreme conditions, and BORO, NPK 7-7-7 and NITRÓGENO 16 write the same instruction: “do not apply at high temperatures”.

Crop condition

A foliar application needs a developed, active leaf. Our data sheets place applications at the “vegetative stage, post-flowering and stages of highest vegetative activity (fruit set, ripening)”, the wording of BORO and of CALCIO 880, which HIERRO and UNIVERSAL repeat with small variations; on frequency, BORO writes “generally weekly applications, between 2 and 4 depending on the crop”. On olive the calendar is written down, with four treatments a year that we summarise below. On almond there is no programme of its own: the BORO data sheet includes it among the fruit trees and publishes for that group “3-6 L/1,000 L per application”, at those same timings.

Which deficiencies are corrected well through the leaf and which are not

The key is the mobility of the nutrient within the plant. Those that move poorly (iron, boron, calcium, zinc, manganese) do not reach the young organs from the root in time, and they are also the ones the soil locks up most easily: a calcareous soil leaves the iron where it is even when there is iron. These are the deficiencies a foliar fertiliser corrects well, because it is applied onto the organ that shows them and in small quantities: HIERRO publishes for fruit trees “2-3 L/1,000 L per application” and, in severe deficiency, “up to 3 applications”; BORO, “3-6 L/1,000 L per application” on fruit trees. What is not foliar is the diagnosis: with boron, the data sheet itself asks to confirm the deficiency by leaf analysis before applying, and we explain it in the boron deficiency guide.

Macronutrients are another case: through the leaf they enter in small quantities and our data sheets dose them as a complement. NPK 9-4-4 publishes by the foliar route “150 g/100 L” on fruit trees and “200 g/100 L” on vegetable crops, and NPK 7-7-7, “2-3 kg / 1,000 L per application”. These are supporting inputs; the bulk of a season’s nitrogen, phosphorus and potassium goes to the soil.

All the products in this guide are suitable for use in organic farming according to the input attestation we publish under certifications: the question of a foliar fertiliser for organic farming has, in our range, the same answer by both routes. How it is checked, product by product, is in the guide to organic suitability.

When fertigation is the better choice

It is the better choice when quantity and continuity are needed: feeding the crop throughout the cycle, supplying humic acids or treating a severe deficiency that foliar feeding cannot reach. It has three rules, and our data sheets write them down.

Split. No data sheet asks to put the whole dose into one irrigation: HIERRO sets “maximum 6 L/ha split, at 10-15 day intervals”; POTASIO K20, “split the input, maximum 6 L/ha, at 10-15 day intervals”; BORO, “split into a maximum of 3 L/ha, at 10-15 day intervals; pre-dilute before pouring into the tank”; HUMIC FULVIC+ALGAS, “split the input, maximum 10 L/ha, at 10-15 day intervals”; NITRÓGENO 16, “split the input, max. 10 kg/ha at 10-15 day intervals”. The 10-15 day interval is repeated in all of them.

Pre-dilute. A dense product, poured as it is into the tank, does not spread evenly: CALCIO 880 asks to “pre-dilute before pouring into the irrigation or spray tank, owing to its density and high calcium concentration”, and FÓSFORO 0-20-0 sets the proportion: “max. 10 L of product per 400 L of water; add an acidifier”.

Acidify. Two products warn of their high pH: HUMIC FULVIC+ALGAS, “owing to its high pH, pre-dilute before pouring into the irrigation or spray tank; add an acidifier”, and POTASIO K20, “owing to its high pH, pre-dilute before pouring into the irrigation or spray tank and add an acidifier”.

There is one limit that no data sheet corrects: the uniformity of the irrigation. An irrigation sector with uneven drippers spreads the fertiliser just as unevenly, and before moving a corrector into the irrigation it is worth knowing how the plot irrigates. In the olive grove, the programme adds two irrigations to the foliar tanks: UNIVERSAL goes at “5 L/ha” in each one, NPK 7-7-7 at “5 kg/ha” in the second, and the data sheet asks for “minimum 3 irrigations”.

Foliar doses across our range, as each data sheet publishes them

This is the table we have not found in any foliar fertiliser guide: the foliar dose of each product, verbatim from its data sheet, with the route and the unit in front of the number. Where the data sheet distinguishes crop groups, all three are given; where it gives a severe-deficiency regime, it goes in the third column.

The table covers the products we deal with in this guide; of those not included, NUTRIPLUS 2,5 publishes only fertigation doses and COMPLEX, from home and garden, publishes no dose table. The units do not convert into one another: “L/1,000 L” is product per volume of spray mix; “L/ha”, product per area; “g/100 L”, a solid that is weighed.

A written example: the four foliar tanks of the olive grove

The olive grove programme is the only one of ours with published doses and a calendar, and it serves to show how timing, route and product intersect. There are four 1,000 L tanks, and the UNIVERSAL data sheet sets their timings: “1st late Feb/early Mar; 2nd one month later; 3rd once the olives have set; 4th ripening; young olive trees monthly foliar”.

1. First, in late February or early March. UNIVERSAL at “3 L per 1,000 L tank”, with PK 20-20, NUTRIPLUS 10 and MICROELEMENTOS; the full tank is in the programme.
2. Second, one month later. The BORO data sheet writes it out in full: “2 litres per 1,000 L tank, mixed with UNIVERSAL 3 L + PK 20-20 1 L + NITRÓGENO 16 2 kg”.
3. Third, once the olives have set. Calcium comes in: “CALCIO 2 L per 1,000 L”, with Universal (3 L) and Nutriplus 10 (2 L).
4. Fourth, at ripening. Potassium comes in: “POTASIO 20: 3 litres”, with Universal 3 L and Nutriplus 10 2 L.

For young olive trees there is a monthly regime: NITRÓGENO 16 at “2 kg/1,000 L, repeat every month”, with Universal 3 L. The four tanks and the two irrigations, with all their doses, are in the olive grove programme.

What not to mix in the tank, according to our data sheets

The incompatibilities we publish are few and specific. HIERRO: “do not mix with phosphate products”. POTASIO K20: “do not mix with highly alkaline products” and “do not mix with products containing phosphorus and/or calcium”; indeed, in the olive grove the calcium goes in the third treatment and the potassium in the fourth. HUMIC FULVIC+ALGAS: “do not mix with highly alkaline products”, nor with alkaline-reaction products and mineral oils. And the line that BORO, UNIVERSAL, MICROELEMENTOS, NITRÓGENO 16, NUTRIPLUS 8, NUTRIPLUS 10, CALCIO 880 and FÓSFORO 0-20-0 repeat as incompatible products: “strong acids and powerful oxidisers”.

When the data sheet is silent on a mix, the rule is that of NITRÓGENO 16: “carry out a phytotoxicity test on a small plot before large-scale application”. And the preparation has its order: “shake the container vigorously before use” (MICROELEMENTOS, NUTRIPLUS 10, POTASIO K20) and “dissolve beforehand before adding to the tank” (NITRÓGENO 16, NPK 7-7-7), which for solids means dissolving separately and adding afterwards.

The two cases in which foliar feeding does not replace the soil

First, total requirements. A crop in production extracts far more nitrogen, phosphorus and potassium than a leaf admits in one pass, and repeating passes is not the answer: the foliar doses of our NPKs are for support; base fertilisation and fertigation are the programme.

Second, the deficiency of soil origin. When chlorosis returns every season on a calcareous soil, foliar HIERRO corrects this year’s leaf and the soil brings it back the next: foliar feeding treats the symptom and soil management (pH, organic matter, water) treats the cause. Our HIERRO data sheet publishes both routes, and the choice is exactly that: the foliar route for the leaf that is already yellowing, the root route for the soil that makes it yellow. The symptom, the cause and the doses are in the iron chlorosis guide.

Frequently asked questions

What is a foliar fertiliser and what is it for?

It is a fertiliser that is sprayed diluted onto the leaf, which absorbs it through the cuticle and the stomata. It serves to correct a specific deficiency in a short time and without depending on the soil; not to cover the total requirements of a crop.

When is foliar fertiliser applied on olive and almond, and how often?

On olive, in the four treatments of the programme: late February or early March, one month later, once the olives have set and at ripening. On almond, as on the rest of the fruit trees, at the “vegetative stage, post-flowering and stages of highest vegetative activity (fruit set, ripening)”, with “weekly applications, between 2 and 4 depending on the crop”.

Foliar fertiliser or fertigation: which to choose?

Foliar to correct a specific deficiency, above all of micronutrients or calcium, quickly and in small quantities. Fertigation to feed the crop throughout the cycle, splitting the input at 10-15 day intervals. The two together are the programme.

Can several products be mixed in the same tank?

Only the mixes the data sheet admits or that a test on a small plot confirms. Our data sheets publish the incompatibilities (HIERRO with phosphate products; POTASIO K20 with phosphorus, calcium and alkaline products) and the tanks of the olive grove programme.

Is there a foliar fertiliser suitable for use in organic farming?

Yes. The products in this guide appear in the annex of the ECOCERT S.A.S input attestation No. 245895/29/290920251037 (“EU - Inputs Attestation” programme), valid until 31 March 2027. The wording is “suitable for use in organic farming”, and the document can be checked under certifications.

The data sheets for all the products cited are in the full catalogue; how to read them line by line, in how to read a technical data sheet. If the question is which route suits your plot, with your soil and your water, the technical enquiry is the place: we answer with the data sheet in front of us.