Holly-Tone Plant Food, 4-3-4, is for acid-loving plants, such as hollies, azaleas, camellias, evergreens, hydrangeas, dogwoods, blueberries, strawberries and rhododendrons. It is rich in natural organics and enhanced with Bio-tone® microbes. Used and recommended by Professionals. Holly-tone's all natural formula contains Bio-tone®, our proprietary blend of beneficial microbes. Bio-tone biologically enhances our natural plant food to ensure superior plant growth.