Espoma Citrus-Tone Plant Food 5-2-6 works well for all citrus, fruit and nut trees. A better option for blueberry bushes/plants and berries (as well as other acid loving plants), would be Holly-Tone. It is best to fertilize at the time of planting or in the spring for established plants before the leaves have grown. Healthy plants should not need to be fed more than once per year. New plants can receive an application in early spring and again in late spring.