Photosynthesis – Why CO₂ Is the Limiting Factor and What That Means for Your Harvest

There is a process that drives everything else. Without it, no growth, no nutrients, no yield. No red onion with quercetin, no tomato with lycopene, no carrot with beta-carotene. No Brix value to speak of.
This process is called photosynthesis. And for most plants in the world, it operates far below its potential.
The reason is surprisingly simple—and so is the solution.

What Photosynthesis Really Is

The CO₂ Problem — Why Plants Are Chronically Undersupplied

Here lies the crucial detail that most people don't know.
Air contains only 0.04 percent CO₂—that's just 400 parts per million. This is extremely little. For a maximum photosynthetic rate, the plant actually needs a CO₂ concentration of 0.1 to 1.0 percent inside the leaf—that is, twenty-five to a hundred times what the atmosphere provides.
This means: under natural conditions, plants are CO₂-limited (their performance is restricted by too little CO₂). They cannot exploit their full photosynthetic potential because the raw material CO₂ is simply not available in sufficient quantities.
Added to this is a fundamental conflict. The plant absorbs CO₂ through its stomata (leaf pores—tiny openings on the leaf surface that open and close). But open stomata also lose water through evaporation. In case of drought stress, the plant therefore closes its stomata to save water—and thereby cuts itself off from the CO₂ supply. Photosynthesis collapses. The Brix value drops. The plant weakens itself at the moment when stress is greatest.
This is not a fringe problem. It is the core conflict of plant physiology—and it occurs daily in every plant on Earth.

What Happens When Photosynthesis Stalls

A plant that receives too little CO₂ operates on a low flame. What this means in concrete terms:

Less glucose is produced.
This means less energy for growth and cell division. Roots remain shallower. Biomass remains lower.
Fewer building materials for cell walls.
Calcium is the main building block of stable cell walls—but calcium can only be effectively incorporated into cell walls if enough energy from photosynthesis is available. Thin cell walls are the gateway for fungal diseases and pests.
Fewer secondary plant compounds.
Quercetin, lycopene, beta-carotene, allicin—all these substances are only formed if the plant has an energy surplus from photosynthesis. A plant operating on a low flame produces the minimum—not the maximum.
Lower Brix value.
The Brix value measures the density of the plant sap—i.e., how many dissolved solids it contains. A plant that performs little photosynthesis has a low Brix value. It tastes less, nourishes less, lasts less long.
Higher susceptibility to pests.
Francis Chaboussou already documented in 1969 that insects and fungi preferentially attack plants with incomplete protein synthesis (protein formation—if the plant cannot form complete proteins)—i.e., plants that perform too little photosynthesis. A plant with a high Brix value (the measure of nutrient density in the plant sap) is simply uninteresting for sucking insects like aphids—its sap contains too many complex compounds that their simple digestive system cannot process.

The Direct Route — Getting CO₂ into the Leaf

This is the basic idea behind Grünkraft Calcium as a foliar fertilizer. And no one has explained it more clearly than Dr. Peter Ost:

"GRÜNKRAFT is a CO₂ fertilizer. The optimal CO₂ content should be between 0.1 and 1.0 vol% for high photosynthetic activity. Air has only 0.03 vol%, which is why plants cannot utilize their optimal growth potential. GRÜNKRAFT increases the CO₂ content in the plant naturally, thus helping the plant to breathe."

The solution is elegant. Tribomechanically activated calcite with zeolite is sprayed onto the leaf. The particles are smaller than 10 micrometers—stomata-permeable (small enough to penetrate through the leaf pores into the leaf interior). They penetrate directly into the leaf tissue through the leaf pores.

There, the calcium carbonate decomposes:

CaCO₃ → CaO + CO₂

The released CO₂ immediately enters photosynthesis. Not at some point. Not after detours via soil and root. Directly. The plant gets the raw material it needs for maximum photosynthesis—regardless of what is in the air outside and regardless of whether the stomata are closed due to drought stress.
The CO₂ in calcium carbonate is reversibly bound—this means: it is not released all at once but exactly when the plant cell needs it. The calcium carbonate releases the CO₂ gradually—controlled by the conditions inside the leaf. With high photosynthetic activity, more CO₂ is released. With lower activity, less. So the plant does not get a one-time CO₂ boost—it gets a continuous, demand-driven supply. This is fundamentally different from simply supplying CO₂-rich air from outside.
This is the bypass. CO₂ directly into the heart of the leaf—exactly as much as the plant needs at any moment.

What Happens Simultaneously — The Calcium Effect

The released calcium oxide is no less important than the CO₂. It performs four functions simultaneously:
Strengthen cell walls. Calcium is the most important building block of stable, dense cell walls. Strong cell walls mean fewer entry points for fungal spores—less Botrytis, less powdery mildew, less scab. A plant well supplied with calcium protects itself.
Regulate stomata. Calcium controls the opening and closing mechanism of the leaf pores. Well-regulated stomata open precisely in light and close efficiently in drought—the plant loses less water and still absorbs enough CO₂.
Improve nitrogen uptake. Calcium stimulates ammonium absorption (the uptake of nitrogen in its plant-available form)—the plant can absorb and process nitrogen more efficiently. This explains the darker, more intense green of treated leaves—they are better supplied with nitrogen, even though no additional nitrogen fertilizer was applied.
Activate defense mechanisms. Calcium triggers a cascade (a chain of consecutive reactions) of defense responses in the plant—from the formation of pathogenesis-related proteins (special defense proteins against pathogens) to the activation of enzymes (protein molecules that control chemical processes) that break down fungal spores.

What Zeolite Additionally Provides

The zeolite in the product also contributes to the photosynthesis effect—in a way that Dr. Peter Ost particularly emphasizes:

"The zeolite particles can capture the sun's rays more strongly on the leaf and thus help to make photosynthesis more active."

The ultrafine silicate particles (finest mineral particles from the zeolite) on the leaf surface act like tiny mirrors that better distribute the incoming light and direct it into the leaf. More light on more chloroplasts (the green cell organelles where photosynthesis takes place) means more photosynthesis—an additional amplifying effect.
At the same time, the silicon from the zeolite activates plant's own defense enzymes—superoxide dismutase, catalase, and peroxidase (enzymes that neutralize harmful free radicals)—which neutralize free radicals (aggressive molecules that damage cells) and protect the plant against oxidative stress (cell damage caused by these aggressive molecules).
And then there's the physical protective effect: the silicate particles on the leaf surface look like tiny shards of glass under a microscope. Insects with tactile organs in their legs find this unpleasant and avoid the plant. The finest particles disturb and block the breathing organs of mites and aphids. This is not a chemical repellent (a repellent that drives away insects)—it is physics.

What Becomes Measurable — The Proof in the Brix Value

The increased photosynthetic activity after treatment with Grünkraft Calcium is not just theoretical—it is measurable. The Brix value of the plant sap measurably increases within 2 to 3 days after treatment.

Why is this so?

Because more photosynthesis produces more glucose—and glucose is one of the main components of the plant sap measured by the refractometer (an optical measuring device that measures the density of liquids). A higher Brix value directly shows: this plant is performing intensive photosynthesis. It is well supplied. It is forming secondary plant compounds.

According to Reams' reference chart, below 7 °Brix a plant is susceptible to all pathogens. Above 14 °Brix, insects cannot tolerate the plant sap. This is no coincidence—it is the direct consequence of a plant that performs intensive photosynthesis and thus builds up its full immune system.
The nutrient-rich tomato with 12 °Brix. The red onion with 10 °Brix full of quercetin. The carrot with deep orange full of beta-carotene. The garlic that smells intensely because it is full of allicin. They are all the result of a plant that had enough CO₂ to fully perform its photosynthesis.

From Plant to Plate — The Crucial Connection

Here the circle closes. And it is a connection that is little known to the public, although it is scientifically well documented.
The secondary plant compounds we find in nutrient-rich foods—quercetin, lycopene, beta-carotene, allicin, sulforaphane, anthocyanins—all arise from photosynthetic energy. They are the surplus that a plant produces when it has enough CO₂ and can perform intensive photosynthesis.
A plant that is chronically CO₂-limited forms the minimum of secondary plant compounds. A plant that is optimally supplied with CO₂ forms the maximum.
The British McCance and Widdowson Study, which documented the decline in minerals in food between 1940 and 1991, is clear: not only have soils become poorer—the photosynthesis of plants on these soils also runs less efficiently, because stressed plants on poor soils close their stomata more often and thus absorb less CO₂.
More photosynthesis is therefore not only an agronomic (relating to agriculture and crop cultivation) goal. It is a nutritional health goal. It is the path from empty calories to true nutrient density.

Why the Tribomechanical Milling Process is Key

Not all calcite can achieve this effect. The difference lies in the manufacturing process.
Conventionally ground calcite—as it is sometimes spread on fields—is too coarse for the stomata. Dr. Peter Ost explains it with an image we always remember:

"You can eat a hamburger because your mouth and the hamburger size approximately match. But if you had a hamburger the size of a soccer ball, it would not be possible to eat it. The lime that is sometimes conventionally spread on the field is on the field, is chemically detectable, but is not available to the plants because it is too coarse."

In the tribomechanical process (an activation process in which mineral particles collide at high speed), calcite particles collide with each other at high speed—up to three collisions per millisecond. The particles are cleaved without destroying the internal crystal lattice structure (the ordered internal structure of the mineral that determines its properties). The result is particles under 10 micrometers that are electrostatically charged by the tribomechanical process.
This electrostatic charge has two effects: The particles adhere optimally to the leaf surface and are not blown away by the next wind. And they are actively drawn into the leaf interior through the stomata by the charge.
This is the difference between a product that is chemically detectable on the leaf—and one that actually reaches the plant.

Why Leaf Shine is the Visible Proof

There is a visible sign that shows whether a plant is truly performing intensive photosynthesis: leaf shine.
John Kempf—one of the influential figures in regenerative agriculture—has described what leaf shine physiologically (at the level of plant physiology—i.e., how the plant body functions) means: Only when a plant achieves an energy surplus through photosynthesis does it store this as fats in the cell walls and as a waxy cuticle (a natural wax layer on the leaf surface) on the leaf surface. This wax film—recognizable by the leaf shine—is at the same time a natural protective layer against pests and fungi.
In other words: a shiny leaf is a leaf that performs more photosynthesis than it needs for mere survival. It has surplus. It builds protection. It is healthy.
Treated plants show this leaf shine significantly earlier and more intensely than untreated ones. This is not a cosmetic effect. It is the visible signal of a plant operating at full capacity.

The Chain from Photosynthesis to Nutrient-Rich Food

Healthy soil → active soil microbiome (the community of all microorganisms in the soil—bacteria, fungi, single-celled organisms) → strong roots → good mineral supply → intensive photosynthesis → more glucose → more secondary plant compounds → higher Brix value → nutrient-rich food → healthy human.
Grünkraft Calcium intervenes directly in the middle of this chain—in photosynthesis. It is the shortest path from mineral to plant vitality. Directly through the leaf. Without detours.
And because photosynthesis is the engine that drives everything else, an intervention here affects all other links in the chain—both up and down.

Sources: Dr. Peter Ost, quote on tribomechanically activated calcite and zeolite as foliar fertilizer | Francis Chaboussou, plant health and pest infestation 1969 | John Kempf, Plant Health Pyramid and leaf shine as a quality criterion | Dr. Carey Reams, Brix reference tables | McCance & Widdowson, mineral decline in British foods 1940–1991