I NEVER EVER water epsom salts into the soil. Too much chance of locking out other nutes.
Instead, fill up a quart spray bottle with lukewarm tap water. Add a pinch or 2 of epsom salts. Swirl to dissolve, and add a drop of dish soap.
Mist lightly, not watering to the point of runoff.
Do this once or twice a day until you notice the symptoms of Mg def (regular, well-defined stripes between the veins) fading back to a healthy green.
Rose bushes like a few pinches of epsom salts sprinkled around the drip line to promote new shoots from the top of the graft.