The easy care Knock Out Roses are heavy bloomers so heavy feeders and so an all purpose plant food like Osmocote Plus is the easy answer to giving them all the micro and macro nutrients that need for the best performance. Many plant foods container just the 3 main nutrients known as NPK or Nitrogen, Phosphorous and Potassium. Osmocote also contains micro nutrients such as copper, iron and more trace elements.  Roses do especially well when supplied with these trace elements. I feed all my roses with Osmocote in the spring and enjoy the blooms all summer and up until frost in the fall. Keep growing, Marianne Binetti