Blossom end rot is when the blossom end of the growing fruit turns dark and begins to decay. The blossom end is the opposite end from where a young, growing fruit is attached to the vine. This can happen to tomatoes, peppers, eggplants and melons. Even a small amount is too late to correct on a fruit, but you can save the plant and grow new fruit.
Blossom end rot is caused by a lack of calcium in the fruiting area of the plant. You can have plenty of calcium in the soil but still have a plant deficient in calcium. This happened to me a few years ago, and I always use a little extra calcium when I plant tomatoes. However, the water line going to the garden from the lake had ruptured, and since there wasn’t enough water, the calcium in the lime didn’t get moved from the soil through the roots. Water is needed to transport vitamins, minerals, amino acids and other nutrients into the plant. As soon as I repaired the irrigation and cut the rotted blossoms off, the new blossoms came out healthy.
If you’re just now planting, place a small handful of lime or gypsum in each hole before planting. If you didn’t use lime or gypsum while planting, you can still go back and apply it to the base of the plant, working it into the soil with a hand tool or short tine rake. Then water it well. Gypsum is calcium sulfate and lime is calcium carbonate. If you don’t want to change the pH of the soil, use gypsum instead of lime. Only calcium carbonate will change the pH of the soil.