I am in northeast Los Angeles, on a slightly sloped part of a hill with 4-10" of sandy clay soil (not much organic matter as there used to be asphalt here 6 mos ago) on top of really hard decomposed granite. It drains very well, but is nearly impossible to dig into with a shovel.

I want to plant several fruit trees/plants (fuerte and reed avocados, snow queen and double delight nectarines, tangelo, bananas and passionfruit). I'm not worried about drainage, but do I need to break up any of the DG to allow the roots to penetrate?

I know you are supposed to dig 3x wider than the root system, but not any deeper and not to disturb the underlying soil. Is this the case even with DG that you can't get a shovel into? Will the roots eventually work their way into it or will the roots be fine just moving laterally? I know avocados have shallow root systems.

I can have a landscaper dig holes with a jackhammer/hole digger, but I want to make sure we're doing it properly.

I am planning to stir in 2" of compost (my own and Gardner & Bloome soil building compost) and lay down a few inches of mulch.

Thank you in advance for any advice.

Matthew

The best tool for this is a pressure nozzle on a pipe, like the landscapers use for boring a tunnel under a sidewalk for running a pipe under this. You find a kit like this at Home Depot that glues on a 3/4" PVC pipe.

I'd add a boatload of compost to it.

The other possibility is to make raised beds of the best topsoil you can find. This could be a mound for each tree or a berm for a row of trees. Bring in as much soil as you can afford, up to about 18-24 inches, and combine it with a good drip irrigation system to rewet that soil frequently. I like the drip tube with built in emitters on about a 12-24 inch spacing depending on soil.

This would also allow you to do some landscapping in the process if needed.

Your current soil sounds too hard to break up with anything short of a backhoe. If a backhoe will do the job you could combine some new topsoil and some loosening of what's there.