Answer: Sounds as though you're describing the symptoms of Blossom-End Rot. This occurs because of too little calcium in the soil, too much fertilizer, very wet or very dry soils (which interferes with calcium uptake, high temperatures, or a combination of these factors. You can help avoid the problem by adding lime to your soil to bring the pH up to 6.8 - 7.2, planting your tomatoes in an area that drains well, mulching the soil, and watering infrequently but thoroughly enough to wet the entire root mass. Tomato plants should be watered thoroughly only about once a week. You can cut off the blackened area and safely eat the rest of the tomato.
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