Espoma Organic 4 lb. 4-3-4 Berry-Tone Plant Food. This all-natural, organic plant food is specially formulated for blueberries, strawberries, and blackberries. It contains Bio-tone, a proprietary blend of beneficial microbes that biologically enhances the plant food to ensure superior plant growth. This long-lasting, slow-release formula is approved for organic gardening and is ideal for feeding berries and other acid-loving plants.