I put a handful of Dolomite lime in the hole with my tomato plants when I plant them. I have never had more than one or two of the earliest tomatoes with blossom end rot. None this year. Dolomite is Ca and Mg. No need for Epsom salt either when using Dolomite.

If my people, who are called by my name, will humble themselves and pray and seek my face and turn from their wicked ways, then will I hear from heaven and will forgive their sin and will heal their land. 2 Chronicles 7:14