Epsom salt provides much needed magnesium and sulfates to your plants. It does not build up in your garden the way fertilizer salts do. Magnesium sulfate is needed for seeds to germinate, and magnesium is critical to the formation of chlorophyll. Your plants need chlorophyll so they can turn the sunlight they receive into food.
A common sign of a lack of chlorophyll is yellowing leaves whose veins remain green.
Tomatoes and roses want 1 tablespoon of Epsom salts per gallon of water/ 2x month.
Shrubs want about 1 tablespoon spread over a 3’x3′ area. So about 1 tablespoon per bush if you don’t have them too close together.
Trees use about 2 tablespoons per tree or 2 tablespoons per 3’x3′ area.
Over the beds use 1 cup per 100 square feet, about 1 cup for a 10’x10′ bed.
The sulfur compounds in Epsom salts also make it easier for your plants to absorb the fertilizers you use.
You can find small containers of Epsom salts in your local pharmacy. Big bags can be found with the lawn fertilizers at the local HD/Lowes/Walmart type stores.