Blossom End Rot
Every year I try to grow tomatoes with little success. The undersides always turn flat and black. A neighbor told me they had blossom end rot. What causes this problem and how can I prevent it?
Blossom end rot is a deficiency of calcium. The problem starts at the bottom of the tomato as a pale, brown spot that turns black and flattens the bottom of the fruit making it look most unappetizing. It's certainly no tomato I would want to eat. We've all heard the old adage, "An ounce of prevention is worth a pound of cure." There are several things you can do to prevent blossom end rot from destroying your tomatoes.
Planting. When you plant your tomatoes add a few crushed eggshells to the planting hole. This will add calcium to the soil.
Watering. Another condition that seems to contribute to blossom end rot is irregular levels of moisture in the soil. Tomato plants take in nutrients, including calcium, through moisture. Inconsistent watering deprives them of these nutrients. So water regularly, every 4 to 7 days is usually sufficient. During droughts or if you are gardening in containers you may need to water every day. To prevent leaf diseases, water the soil, not the leaves, keeping the foliage as dry as possible. To keep the soil consistently moist, cover it with a 2 to 3 inch layer of mulch. You'll find this also helps keep weeds down. Keep the mulch away from the stem of the plant.
Spraying. Now these are things you can do for your plants at the time of planting or when they are young. Once the plants mature a bit and actually set fruit, another thing you can do is spray them with liquid calcium. This is readily available at garden centers and nurseries. Just follow the directions on the label and spray it directly on the plants.