How to Fix It
What it looks like:
The tomato plants appear healthy, but as the tomatoes ripen, an ugly black patch appears on the bottoms. The black spots on tomatoes look leathery. When you try to cut off the patch to eat the tomato, the fruit inside looks mealy.
What causes it:
Your plants aren’t getting enough calcium. There’s either not enough calcium in the soil, or the pH is too low for the plant to absorb the calcium available. Tomatoes need a soil pH around 6.5 in order to grow properly. This soil pH level also makes it possible for them to absorb calcium. Uneven watering habits also contribute to this problem. Hot, dry spells tend to exacerbate blossom end rot.
What to do about it:
Before planting tomatoes in the spring, conduct a soil test. If you have had problems with blossom end rot in the past, add a proper amount of lime and gypsum for calcium depending on your soil’s condition. That’s why a soil test is necessary. Adding crushed eggshells to your compost pile can also boost calcium naturally when you add compost to the soil.
A foliar spray containing calcium chloride can prevent blossom end rot from developing on tomatoes mid-season. Apply it early in the morning or late in the day, if sprayed onto leaves midday, it can burn them. Water plants regularly at the same time daily to ensure even application of water.