Perennials and Miracle grow
Miracle grow is fine for annuals however with perennials you must amend the soil. Mix in compost into the soil between the plants, pull away the mulch and add some around the base of the plant. In the fall mix in some cow manure. Perennials are generally easy to grow however they need to get their nutrients from the soil and if you are only using miracle grow your perennials have used up all the nutrients that the soil had and will not produce flowers.
Hope this helps you and your garden.