Fruits sprayed with calcium will stay firmer even after harvest. Because calcium forms part of the structure of cell walls, it is an important element that can drastically influence apple quality. Fruits with low calcium have weaker cell walls and, as a result, are softer and more prone to disease. Several formulations are being marketed as safer and more effective than calcium chloride. Most studies have shown that there is no difference in fruit quality, bitter pit incidence, or senescent breakdown between calcium chloride and other formulations.
Calcium chloride is the cheapest source of calcium.
The high nitrogen in this formulation may reduce fruit color in some varieties. Trees should be sprayed with calcium every two weeks until harvest. The rates and timing may be adjusted, but growers should attempt to apply the equivalent amount per acre per year. If you use calcium nitrate, the rates will be 4 to 5 lbs per 100 gallons dilute until harvest. When calcium chloride is used, the pH of the spray solution must be adjusted to approximately 6.7.