It’s amazing just how many of the the roots you can chop off and still get such prolific growth on these tridents.
Not all species can be treated like this but most are far more tolerant of root pruning than most people believe.
There is a perception that pruning roots slows growth. I noticed it can actually accelerate growth. My bonsai all grow far stronger in the year following repotting. Growth then slows gradually as the pot fills with roots. Many people refuse to believe even though the evidence is in front of them. Such is the power of preconceived ideas.
Preparing the ground is much like a bonsai potting soil. Everyone will have a different starting base (soil) and different ideas of what should be done to improve it.
My base soil is really nice friable decomposed granite with a good amount of red soil to give good fertility. To that I added a couple of loads of commercial compost to improve the structure and add nutrients. Every few years I add more composted manures to maintain nutrient levels. I also mulch heavily each summer which gradually decomposes adding more organic matter and nutrients. I run the rotary hoe through the beds to break up the soil and mix the soil before planting.
If the soil would grow good vegetables it should also grow good trees.
A less fertile soil will still grow trees, just a little slower.
Friable soils are easier to work with and far easier to dig and clean the roots. Trees will grow in clay but is can be really hard to get off the roots when you need to root prune or change the soil to a bonsai mix for pots.