The firmness of the blueberry It comes down to a more precise question than just the presence of calcium: how much of that calcium reaches the structures that support the cell wall and how it relates to magnesium and potassium during fruit development.

That was one of the main points raised by Reinaldo Campos, from the University of Chile, during Blueberries Mexico 2026, in a presentation focused on the strategic management of calcium, magnesium and potassium for fruit firmness and quality.

His presentation steered the conversation toward the value of nutritional balances. In a market demanding firmer, larger, and better-quality fruit, Campos connected genetics, environment, and management with a practical idea for producers and technical teams: the quality of the blueberry It is defined from early decisions that influence cell structure, nutrient transport and fruit behavior at harvest and post-harvest.

Quality, variety and atmosphere

Campos noted that blueberry quality parameters have changed significantly. Current requirements for firmness, size, Brix levels, and fruit condition are higher and are linked to the development of new varieties and more selective markets.

From that basis, he explained that each quality attribute results from the interaction between variety, environment, and management. Genetics provides a potential; the environment can favor or strain its expression; and management defines how much of that potential ultimately reaches the marketable fruit.

Under conditions of high temperatures, water scarcity, or poor water quality, this relationship becomes even more critical. The plant needs to maintain carbon and water balances to produce sugars, build reserves, and fuel fruit growth. When these processes are strained, yield, size, firmness, and final quality can also be negatively affected.

Reinaldo Campos at the XLI International Blueberries Seminar Mexico 2026 © Blueberries Consulting

Calcium that truly provides firmness

One of Campos's key contributions was distinguishing between the presence of calcium and functional calcium for firmness. The researcher explained that calcium linked to consistency is located in the cell wall, where it participates in the binding of pectins and in the formation of a structure capable of providing flexibility, resistance, and firmness to the fruit.

This distinction changes how nutritional analyses are interpreted. A sample may show calcium in the plant or fruit, but the quality value appears when that calcium is found in the fraction associated with the cell wall.

For growers and consultants, this point is relevant because it helps to interpret nutritional programs more accurately. The goal is no longer just to confirm the presence of the nutrient, but to understand whether management practices are promoting its incorporation into the structures that directly affect firmness, weight loss, and fruit condition.

Calcium: context-dependent responses

Campos presented background information linking calcium applications to improvements in fruit firmness at harvest and post-harvest, including experiences where post-harvest fertilization showed effects in the following season. He also reviewed early foliar applications that, in some studies, successfully modified fruit firmness.

The researcher maintained a cautious approach. The response to calcium can vary depending on the application method, concentration, timing, variety, and growing conditions. Regarding foliar applications, he mentioned positive results, along with reviews showing inconsistent or insignificant effects.

This nuance adds technical value for the industry. Calcium has a clear physiological basis in firmness, but its productive impact depends on how it is integrated into the management program, the timing of its application, and its effective delivery to the cell wall.

Reinaldo Campos at the XLI International Blueberries Seminar Mexico 2026 © Blueberries Consulting

When magnesium and potassium change the calcium reading

The most strategic focus of the discussion emerged when Campos steered the conversation toward the interactions between calcium, magnesium, and potassium. All three are essential cations, perform distinct functions, and can compete in processes of absorption, transport, and accumulation.

Campos explained that the amount of each nutrient must be considered in conjunction with the ratio between them. This interaction can modify how the plant absorbs and distributes calcium, thereby affecting its ability to reach the cell wall.

To explain these antagonisms and equilibrium points, he also used models from other species, a decision he justified by the limited availability of specific information on blueberries, and especially on new varieties. This caution is relevant: models can guide the discussion, but the final adjustment must be made using information on the crop, variety, environment, and production system.

In intensive systems, a program with high potassium or magnesium levels requires careful consideration of its relationship with calcium, especially when the goal is to maintain firmness. The key lies in managing the ratio between cations, rather than increasing one element in isolation.

Reinaldo Campos at the XLI International Blueberries Seminar Mexico 2026 © Blueberries Consulting

Opportunity for application and development of the fruit

Campos also highlighted the role of the timing of application. In the case of calcium, a significant portion of its movement to the fruit occurs in early stages, when the xylem still contributes to its transport. As the fruit develops, this dynamic changes, while potassium and magnesium follow different curves.

This difference has direct implications for management. The nutritional program must consider how much to apply, when, at what cation ratio, and with what fruit objective. The timing of application becomes as important as the concentration when the goal is to influence firmness, size, and quality.

The researcher also linked these balances to vegetative growth. Excessive vigor can increase competition between leaves and fruit for water, nutrients, and transpiration. In the early stages of fruit development, this competition can influence processes that later manifest during harvest and post-harvest.

For producers and exporters, this reading connects nutrition, physiology and the market: firmer fruit responds to management capable of balancing growth, nutrient transport, cell structure and commercial objective.

Nutritional balances to support consistent fruit

The presentation provided concrete insights for producers, consultants, and technical teams of blueberryCalcium, magnesium, and potassium should be managed as part of a nutritional balance focused on firmness, condition, and fruit quality.

Calcium remains a key element for firmness, and its impact depends on its location, timing, and relationship with other cations. Magnesium and potassium fulfill essential roles, and their management must consider how they interact with calcium incorporation in quality-related structures.

In a market that demands greater caliber, firmness, and consistency, the nutrition of blueberry It gains value when designed based on balance, opportunity, and business objective. Campos' contribution was to shift the conversation from nutrient application to how calcium, magnesium, and potassium interact to support firmer, more consistent, and reliable fruit.

Check out the interview with Reinaldo Campos at the XLI International Blueberries Seminar Mexico 2026 on our YouTube channel Blueberries TV 

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