This year's Yum Yums hybrids are looking decent at 4 weeks.
Just translated them into 4 inch pots and gave them their first fertilizing (other than what I added to my soil mix).
If it's pure Epsom Salts, it should be nothing more than Magnesium Sulfate.
Magnesium Sulfate is a Micro-nutrient, so plants don't need much of it.
Most all soils contain a sufficient amount of Magnesium for plants as long as it's healthy and contains organic mater.
A good way to add Magnesium...
That depends on your soil, most soil types don't really need added magnesium.
Unless you get tons of rain, your soil in extremely high in potassium or you have very sandy soil you shouldn't need to add Magnesium. A good soil test will tell you if you would befit from added magnesium or not...
Only if your soil in depleted in Magnesium, keep in mind Magnesium is Micro-nutrient plants need very little of it.
Increasing Magnesium around the root zone can in fact cause Blossom End Rot just the same as too much Ammonium Nitrate or the lack of Calcium in the soil or the lack of Calcium...