I use the fertilizer that Simon and I suggested. Gro power citrus avocado fruit 8 6 8 for all my fruit trees. Its 40% humus which will improve your soil and its got micros and no manures. Very good fertilizer. For potted plants osmocote plus.
I have half a dozen citrus, half a dozen guavas, 10 annonas, 25 avocados, 10 mangos, a handful of euginias, 4 bananas, grapes, passion fruit, peach, persimmon, cherry, several apples, nectarine, litchee. Lots of plants, lots of fertilizer. All of my plants are young as we have only lived here 3 years.
The soil here is decomposed granite. It drains well and has pretty much no organic matter. It gets washed out and depleated and needs fertilizer. Ive seen other soil types in san diego that are a lot more rich. Member GregA in Ramona has a loamy blackish soft soil and uses only mulch and his chickens poop for his yard and does fine. He doesnt use any store fertilizer and his trees are all loaded. The other type of soil you see in san diego usually in housing developments is clay/bedrock where they excavate to make a neighborhood. Its hard (rocks) doesnt drain well and not super rich. That stuff can benefit from compost/mulch and maybe gypsum. For your trees to really utilize your fertilizer, they need a decent soil and they need good sun and good watering. If your plants are sitting in the shade and not getting sun energy, throwing more fertilizer isnt going to make them grow. If you have the basics (soil, sun, water) met then fertilizer can help. Otherwise it can be a waste or money or even worse burn your plants. The place I used to live had poor sun penetration (few hours of full sun per day) and bedrock/clay soil. Nothing would grow there and fertilizer wasn't going to fix that. All my trees died at that house. New house gets full sun and good draining soil, everything grows here.
Hope that helps.