Pros and cons on using bonsai mix vs nursery organic soil on trees in development / pre-bonsai.

1. Best way to develope a tree is to plant it in the ground. But lets say you can't.
2. For a healthy tree, the roots need equal amount of water and oxygen. Organic soils tend to stay wet for too long, bringing the oxygen level down.
3. You can't overwater with bonsai mix so no rootrot problems. But you need to water the trees more often.
4. Everything organic will degrade and you will need to replace the soil and disturb the roots more often than with inorganic bonsai mix.
5. Akadama is the best medium to refine the roots. You need fine feeder roots, not thick taproots for the tree to grow vigorously and the growth is controlled with the amounts of fertilizer. Fine feeder roots don't restrict the growth.
6. It's easyer to repot a tree planted in bonsai mix. In the final stage of a bonsai you need to replace the organic soil anyway and it will take years unless you bare root and kill the tree. Better replace the soil slowly allready in development.
7. Most nurserys use peat and peat based organic soils because it holds water for a longer time. They have a lot of plants in the nurserys and with peat they don't have to water them as often. The trees are usually in full sun and on black tarps so the trees need more water.

I will add one.

Weeds are easier to pull from a mix with mostly large pieces of lava rock, pumice, and akadama.

Drop #5 as it is nonsense.

Replace by, avoid substrates that are heavy on akadama in moderately cold climates as it breaks down to mud over repeated frost-thaw cycles

Yes, akadama breaks down a lot faster than a good organic mix in my climate. So if breaking down is an issue, akadama is out of the question here.

I can't edit it anymore. I didn't know akadama breaks down so easily with frost, I thought it only breaks down actively because the roots grow through it. What temperatures does akadama dolerate without freezing and breaking?

Freezing is the point when it breaks down. For every freeze thaw cycle it breaks down a little bit more. In my climate it could be every day/night for a month in athum and a month in spring.

If you have constant zub zero temperatures the problem might be less.

Hard Akadama only breaks down in my climate after three or four years.

If only more experts would share information like this. I watched the BSOP soils episode on youtube. Ryan from Bonsai Mirai explained everything very detailed, scientifically and most importantly why it's done this way. Healthy roots need equal parts of water and oxygen.
Peter Chan from Herons Bonsai says you need fine feeder roots, because these are the ones that provide the tree with most of the nutrients. Thick taproots are just to anchor the tree and to find water and nutrients deeper in the ground if the top soil is dry.
2+2= for growing the tree healthy, bigger and thicker, I need a balance of water and oxygen and fine feeder roots and heavy ferting from spring to end of summer.
Not one expert has mentioned that you need thicker roots and organic soil for developing a tree until yesterday someone shared this video to me (scientifically I still haven't found any explenation)

Organic soil.

Most mixes are non-organic akadama, non-organic lava rock, and non-organic pumice, or a replacement for akadama which is just as non-organic. Back before the days of the current philosophy we used sand and similar stuff.

Here in the south we tend to put some organics in the soil mix simply to hold more water, but I don't know how effective that is. Usually about 10%, and some use ground up pine bark or similar.