Tomato fruit cracking essentially occurs due to one main reason and that is uneven watering. Other factors may play into it but if your tomato plant's root system severely dries out and that is then followed with lots of water... tomato fruits often crack. The roots try and send in too much water too quickly to the fruit and they crack.
If your container tomatoes dry out completely, don't flood the container with water. It probably will cause the fruit to crack. Give it a little water through out the day and let it slowly drink up. After a full day or two of a little water, you can go back to a regular watering routine.
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