fruit trees in HARD decomposed granite
I have a question about how to prep the ground for several fruit trees.
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.