Foliar calcium: the problem is not applying it, it is getting it into the fruit
Calcium is the one macronutrient that barely moves in the phloem. It travels with the transpiration stream, and fruit transpires little: a leaf can therefore be well supplied while the fruit goes short. Applying more solves nothing if it does not arrive. This page deals with the two questions that actually decide: how much calcium ends up inside the fruit, and which ion comes along with the calcium you apply.
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more calcium in the fruit: from 55 to 140 ppm — Holden Research, Arizona
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more penetrometer firmness: from 5.99 to 7.06 lbs of pressure
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laboratory-measured calcium oxide in CALCIUM 40
Why calcium reaches the leaf and not the fruit
Calcium moves in the xylem, carried by the transpiration stream, and is barely redistributed through the phloem. The organs that transpire most — leaves — receive most of it; those that transpire least — fruit, and especially young expanding fruit — receive far less. A leaf analysis can therefore come back fine while the fruit is short of calcium.
So the useful question is not how much calcium you apply, but how much ends up inside the fruit. That is what was measured in Arizona, and it is the only way to know whether a foliar application did anything at all.
The companion ion decides as much as the calcium
The cheapest foliar source is calcium chloride, and every kilo of calcium brings about 1.77 kg of chloride with it. Calcium nitrate carries no chloride but adds around 15.5 % nitrogen — precisely what you do not want during ripening. CALCIUM 40 measures chloride below the detection limit and adds no nitrogen.
Particle size matters in foliar application
CALCIUM 40 is a suspension of micronised calcium carbonate below 1 μm. In a spray, a particle that size spreads and adheres differently from a coarse soluble crystal; the product declares and measures it, and the figure is on the datasheet.
pH determines what it can be mixed with
CALCIUM 40 has pH 7.99, essentially neutral. That matters because calcium precipitates with phosphates and sulphates in the tank: loading order and incompatibilities are checked pair by pair before preparing the spray.
Calcium does not cure a disorder, it nourishes
Calcium deficiency in fruit is associated with known physiological disorders, but a fertilizer is not a plant protection product and is not claimed as one here. What is claimed — and measured — is the nutritional function: how much calcium is in the fruit.
Chloride entering per kg of calcium
Shorter is better. The two grey sources are market reference compositions, not our own measurements.
| Calcium source | kg Cl per kg Ca | Note |
|---|---|---|
| CALCIUM 40 | < 0,002 kg Cl / kg Ca | — |
| Nitrato cálcico | 0 kg Cl / kg Ca | — |
| Cloruro cálcico (CaCl₂) | 1,77 kg Cl / kg Ca | — |
- CALCIUM 40 — 34,0 % CaO · < 0,05 % · cloruro por debajo del límite de detección
- Nitrato cálcico — ~19 % Ca · 0 % · sin cloruro, pero aporta ~15,5 % de nitrógeno
- Cloruro cálcico (CaCl₂) — 36,1 % Ca · 63,9 % · la fuente foliar más barata del mercado
What was measured inside the fruit
Three seasons with a commercial melon grower in Arizona. What makes this trial useful is not yield: it is that it measured calcium inside the fruit, which almost nobody measures.
CALCIUM 40 % PLUS applied at 1.0 gallon/acre in four applications, from first fruit set and repeating every 7 days for one month, through subsurface drip irrigation. In the 2010 season BOOST UNIVERSAL was added at 4 oz/acre per application.
Fruit calcium (ppm)
| Calcium source | kg Cl per kg Ca | Note |
|---|---|---|
| Testigo sin tratar | 55 ppm | — |
| CALCIUM 40% PLUS | 140 ppm | +155 % |
Penetrometer firmness (lbs)
| Calcium source | kg Cl per kg Ca | Note |
|---|---|---|
| Testigo sin tratar | 5,99 lb | — |
| CALCIUM 40% PLUS | 7,06 lb | +18 % |
Fruit calcium rose from 55 to 140 ppm and penetrometer firmness from 5.99 to 7.06 lbs. The two figures belong together: firmness rises because the calcium arrived, not the other way round.
A trial series with a commercial grower, not a university randomised block design. The trial names the product «CALCIUM 40 % PLUS»; in the current catalogue the reference is CALCIUM 40. We publish it with that precision.
Holden Research and Consulting — Arizona (USA), 2008-2010 seasons
See all 24 published trials →CALCIUM 40, as declared
| Value | Figure |
|---|---|
| Calcium oxide (CaO) | 34.0 % w/w (measured) |
| Calcium (Ca) | > 25 % w/w |
| Micronised calcium carbonate | particles < 1 μm |
| Freshwater microalgae extract | 25 % w/w |
| Chloride | < 0.05 % (below detection limit) |
| pH | 7.99 |
| Density | 1.624 kg/L |
| Rate | Foliar 2–3 L/ha or 200–300 cc/100 L · Fertigation 5–6 L/ha |
Frequently asked questions about foliar calcium
Why does calcium not reach the fruit?
Because calcium moves in the xylem with the transpiration stream and is barely redistributed through the phloem. Leaves transpire heavily and receive most of it; fruit transpires little, and young expanding fruit less still. A sound leaf analysis therefore does not guarantee that the fruit has calcium.
How much chloride does calcium chloride add?
Anhydrous calcium chloride is 36.1 % calcium and 63.9 % chloride: roughly 1.77 kg of chloride per kg of calcium. It is the cheapest foliar calcium source on the market and also the one that introduces the most chloride, which makes it problematic in avocado, citrus, blueberry, strawberry and vine.
How does it differ from calcium nitrate?
Calcium nitrate adds no chloride but does add around 15.5 % nitrogen. During vegetative growth that can suit; during ripening it usually does not, because nitrogen delays colouring and softens fruit exactly when you want the opposite.
How much calcium and how much chloride does CALCIUM 40 have?
It declares 34.0 % laboratory-measured calcium oxide and over 25 % calcium, in a suspension of micronised calcium carbonate below 1 μm with 25 % freshwater microalgae extract. Its chloride is below the detection limit (< 0.05 %) by ion chromatography to UNE-EN 10304-1 at an ENAC-accredited laboratory.
Is there any measurement that calcium actually reaches the fruit?
Yes. In a trial series by Holden Research and Consulting with a commercial melon grower in Arizona (2008-2010), fruit calcium rose from 55 to 140 ppm and penetrometer firmness from 5.99 to 7.06 lbs. It is a commercial-grower series, not a randomised block design.
What should calcium not be mixed with?
Calcium precipitates with phosphates and sulphates. CALCIUM 40 has pH 7.99, essentially neutral, but tank loading order and incompatibilities are best checked pair by pair before preparing the spray.