Mary Beal wrote:

This is the 2d year my tomatos have dark spots (big) on the underside.
Someone told me I water too much. Someone else told me I water too little!
I am not convinced it is the watering. Maybe something in the water? We
have a well.

Would appreciate anyone who knows weighing in.

Mary


It is caused by a calcium deficiency in the fruits. Indirectly it is
caused by moisture stress that can make whatever calcium is available
accumulate in the leaves and not the fruit.

Maintaining uniformly adequate soil moisture is the key. Adding a little
calcium chloride or calcium nitrate to the soil couldn't hurt. You can buy
a calcium chloride product called "Stop Rot" that says to apply foliarly.
It works a lot better to water the the roots with it. Adding a little
epsom salt to supply magnesium might also help the plants use their calcium
more efficiently.

Best regards,
Bob