When to fertilize and Epsom salt tomatoes

Mine are just tall enough to tie to stakes but are a little pale green. When should fertilizer(what type) and when should Epsom salt be applied. Also how often

I sprinkle Epson salt on my tomatoes once a month. I only fertilize during planting.

I put epsolm every two-three weeks but i have major problems with blossom end rot. I fertilize usually the same time.

I use 13-13-13 and side dress the plants, I do not apply before planting. I put out epsom salts every couple of weeks unless we have a lot of rain(like this year) then I put it out a day or so after the hard rain, at least once a week.