Blossom end rot
I have blossom end rot in my green zebra tomatoes I have in a pot. Any suggestions? I have fertilized pretty lightly with organic tomato fertilizer. Other potted tomatoes are various cherries and have been fine. Lime?
Blossom end rot, often abbreviated BER, is a physiological disorder caused by the inability of the plant to transport calcium to the far end of the tomato.
The lack of calcium is sometimes due to low calcium in the soil (or potting mix) but is more often due to erratic moisture in the growing medium. Some kinds of tomatoes, such as Roma, and all kinds grown in containers, are more likely to be affected by BER than are tomatoes grown in the ground.
The remedy for your container-grown tomato is to ensure that the potting mix is evenly moist. Temporary shade can help during a heat wave when, even if the soil is moist, the plant may lose water faster than it can absorb it.
It’s true that lime supplies calcium but it’s unlikely to be needed in the container. The most important factor for your tomato is an even supply of moisture to the roots. If temperatures soar, temporary shade will slow water loss from the plant.