Yes, Epsom salt will add magnesium to the soil and this is a limiting nutrient in some soils. However there are many nutrients and micronutrients that plants need especially roses. When you use a complete plant food that contains the big three nutrients of nitrogen, phosphorus and potassium plus the many trace elements such as copper, calcium and many more you are insuring that your plants have all the nutrients needed for proper growth. Some roses like the Knock Out roses are called 'self cleaning' because the petals fall from the open flowers soon after they fully open and flower. These landscape roses are grown for their multiple buds and numerous flowers and not as cut flowers that last in a vase. Keep growing, Marianne Binetti