Question: What causes the sunken brown spots on the bottoms of my tomatoes?

Answer: That’s a physiological disorder called blossom-end rot. It has been attributed to a lack of calcium in the soil, but you’ll see it in soils that are quite high in calcium. The fact is, you seldom see blossom-end rot until it gets really hot and dry in the summer. The soils have the same amount of calcium in late spring as they do in the summer, yet the problem doesn’t show up until it’s hot and the plants are using water most rapidly, so there are obviously other things going on. Generally, it happens when we let our tomatoes get too dry between waterings. Just as leaves turn brown and crisp at their ends when they have gotten too dry, fruit will do the same thing. Try mulching the plants and watering them more religiously, and see if the problem doesn’t resolve itself.