Answer: Epsom salts are a highly water-soluble form of magnesium sulfate. As a result it should not tend to build up in soils or cause soil pH to change much. If too much were used, a good drenching with water would tend to wash it away. Also since it doesn't contain sodium, it would not contribute to sodic soil conditions. Magnesium, when applied in excess, could cause a deficiency of certain other positively charged elements in the nutrient solution such as potassium or calcium.
Here is the suggested epsom salts rate for roses from the Epsom Salt Industry Council (yes there is such an organization!):
"Sprinkle 1 teaspoon per foot of plant height and spread evenly around the base for better blossoms and deeper greening."
"Add 1/2 cup sprinkled around the base and then scratched in, for strong production of new flowering canes and healthy new basal cane growth."
Q&A Library Searching Tips