I've posted this every year for the last umpteen years, but if you'll put 1/2-1 cup of Dolomitic Lime in the soil mix around your tomato plant you will have no blossom end rot.
A scoop of pelletized chicken shucks in the hole then sprinkle around every few weeks will keep it from happening to. Just doesn’t feed it potash but gives a little nitrogen and lots of calcium.
