The affected tissue breaks down rapidly and the area becomes sunken, dark brown or black, and leathery. This can happen at any time as the tomatoes mature, and most often on the first tomatoes of the season. Blossom-end rot is caused by insufficient calcium in the tissue of the tomato. This means that the rot can occur even when there is an ample supply of calcium in the soil, stems or leaves. Actively growing parts of the plant such as developing tomatoes must have a continuous supply of calcium to prevent these spots from developing.
Blossom End Rot on Tomatoes, Eggplants, and Peppers
Why are your tomatoes rotting on the bottom? Unfortunately, they likely have blossom-end rot. Blossom-end rot is caused by a lack of calcium in the plant. This lack of calcium may be due to low calcium levels in the soil, or due to soil that is over- or underwatered. Some blossom-end rot is more or less normal in the first tomatoes of the season, since the plants are usually under stress during the initial fruit set.
The first sign is a brown discoloration near the bottom end of the fruit. These spots grow and darken until they cover up to half of the tomato, and the rotting fruit becomes vulnerable to secondary bacteria and fungi. The affected tomatoes can't be saved, but the plant can. Blossom end rot is the result of calcium deficiency. However, that doesn't necessarily mean that you need to add calcium to your soil.
Who put this disgusting black scab on the bottom of my beautiful tomato? Blossom end rot is caused by two things: a lack of calcium and inconsistent watering. However, you can still save the plant and any remaining tomatoes it produces. Put all rotten tomatoes in your compost and cut your losses.