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.

If always been told it has to do with calcium absorption and/or
magnesium in the soil. HOWEVER, I'm not an 'additive' person and the
first year I started mulching well around the plants, ALL the blossom
end rot stopped, and I haven't had it since.

I use no chemicals on my plants nor on my lawn. I mow my lawn and then
put the lawn clippings thickly (6" or so) around the base of all the
tomato plants, leaving a few inches around the main stem so the grass
doesn't touch it. This type of mulching, btw, will also keep the
moisture even in and around the plant, so it'll help if any of the
blossom end rot issues are from water absorption or lack thereof.

hth, Bobbett