It sounds like you have a different take on the forest gardening problem, one that works.
Are you tired of the need to garden in containers?
I happen to have two mulberry trees next to my very large chicken composting yard and they grow a network of roots deep into the pile.
I accept it as gift , because they don't seem to sprout from the root fragments and living roots feed soil organisms.
I will be trying to establish elderberry along the edges of that pile, for their alleged compost accelerating properties.
I most falls I create compost bins out of pallet wood, often right under the fruit trees I favor.
I fill the bottom with woody biomass, followed by leaves and urine.
I plant tomatoes and squash transplants into the unfinished compost, water and walk away.
Later I harvest what's there, and add a deep layer of leaves/urine.
I repeat this cycle until the pallets start to rot ,then I harvest the compost, taking whatever isn't fully decayed and adding it the bottom of a new compost bin/ garden bed.
The tree roots tend to stay in the soil proper, probably because so many nutrients are leach into it from above.
This method or some variation might free you from the need for actual containers, though I've found these beds are good places to put containers of seedlings, to keep them from drying out.
I've recently built a table style bed at my mother's house.
The top of the soil is about 30" off the ground.
It has already produced a flush of turnip greens, from transplants that had been languishing in a ground level bed.
