Epsom salts contain hydrated magnesium sulfate, two trace elements crucial to plant growth: Sulfur (important to the inner workings of the plant) and Magnesium (which can become scarce in soil due to erosion of the top soil or pH imbalance). By providing Epsom salts for your roses you will encourage sturdier stems, richer green foliage, and deeper, rich petal colors. You can purchase it in appropriate quantities at a feed store if you have a lot of roses to feed, or you can pick some up at your local grocery store. During the first-year, use just a teaspoon or two in the early spring. For mature bushes, use half a cup at the drip line.