Potassium is the key driver of fruit size and alongside nitrogen is required in large quantities throughout fruit development and growth. However, too much nitrogen at a late growth stage can restrict fruit size; therefore a balanced nutrient application is crucial. Phosphorus can restrict fruit growth too.
Iron and zinc supply also positively influence fruit size, increasing crop yields.
Trials confirm that the improved yield from potassium is due, in part, to reduced fruit set but mainly as a result of an increased fruit size.
According to the trials taken in Florida on sandy soils susceptible to potassium leaching, foliar K applied in the fall increased fruit size of Marsh Grapefruit.
Trials have shown that micronutrients like iron, manganese and zinc will affect the final fruit size. Lack of zinc, for example, results in smaller, misshapen fruit.
Citrus fertilizer program?