Take a soil test and it will spell out just what you need. There's no need buying something that the soil doesn't need. Contact your local ag extension agent and he can tell you everything you need to know. Might need to adjust the ph up or down, more or less nitrogen, more or less phosphate, more or less potash.
I just throw out some 19-19-19 or 6-12-12 around my trees (only got 5) when I am planting in the garden but then the soil around here is pretty poor, red clay.