This problem, called blossom end rot, is seen every year here on tomatoes and sometimes peppers and eggplant. No one really knows the exact cause for this physiological “disease” but scientists agree it probably comes from mineral imbalances inside the fruit. The mineral usually associated with blossom end rot is a lack of calcium.
|Blossom end rot of tomato|
On the East coast, in acidic soils, the recommendation is to “lime” the soils or add calcium carbonate to the soil so the plant does not “run out” of calcium. But calcium sprays applied to tomatoes do not cure the problem.
|Blossom end rot of pepper, frequently confused with sunscald|
This is odd because calcium sprays such as calcium chloride applied to the fruit of apple and pear trees cure their calcium deficiencies, namely “bitter pit” and “corky spot”, and work in southern Nevada.
|Corky spot of Keiffer pear, corrected with calcium sprays applied to the fruit|
Until scientists understand blossom end rot better, we are stuck with the same old recommendations that I am going to repeat here and can be found elsewhere.
Don't waste your money on calcium sprays. They don't work. Focus your energy on mulching vegetable beds to prevent water stress in the plants. Monitor your irrigations so that plants do not become water stressed.