Hi, everyone! I'm a new member and relatively new to bonsai (started a couple years ago).
When I started with my first few trees, I quickly put them into bonsai pots and started pruning and refining, etc. With my new trees this season, I want to give them more time in development to grow their trunks and manage their structures.
I got two new trees today from a nursery, both quite small--a Hokkaido Chinese elm and a barberry. I'm going to move them into larger nursery containers, but my question is: What kind of soil should I use for development? Is a partial organic mix better than the inorganic soil I use for my bonsai in refinement? The nursery mix seems to be potting soil with pine chips. Is that just standard nursery practice for any plant, or is that the kind of mix I want them in for development?
Would love to hear what you all do, and any other advice on good development practice.
I'm not an expert but I'll give you my feedback since no one else has yet.
I'm assuming you are putting them into the standard relatively tall nursery containers. In that case, the soil column drains better/more quickly (and aerates better/more quickly) than in a shallow bonsai pot. Therefore you can use a mix that retains water better than a pure inorganic bonsai mix.
If it were me (I am retired and can water 2-3 times per day), I would still use a mostly inorganic bonsai mix. That way you can water more often and the tree will metabolize and grow more quickly. But, if you can only water once a day, go with a more organic mix that retains water. I really like pine bark chips (with the fine particles sieved out) as an inorganic component.
Don't repot your trees into a too big container, especially if you use an inorganic bonsai mix. If the rootball is "swimming" in a bonsai mix in a very large container, new roots wont grow into the dry bonsai mix and the existing rootball will stay wet (and not get enough oxygen) and the tree will suffer. Aim to pot it in a container that is 10-15% larger by volume than the current container. There should be about 1/2 to 1 inch of bonsai mix around the existing rootmass.
Hope this is helpful and good luck,