Grow bags vs Anderson Flats vs Box vs Pots

I’m trying to get my garden (and life…) organized so I need to come up with a plan. I have quite a number of small trees and shrubs in pots that I would like to start training as bonsai. There are so many different approaches to growing pre bonsai and I haven’t really seen a discussion about the merits of each all in one place so I thought I’d ask here and see what people think.
I have a dozen or so in-ground grow bags, a dozen Anderson flat deeps, I can make plenty of wooden boxes and I have a number of hypertufa pots that I’ve made myself. My question is which species go where?
My current thinking is that I will grow the smallest conifers in the ground in root control bags to increase the size, the medium sized trees (conifers and deciduous) I will put in Anderson flat deeps to start encouraging lateral roots and shallow feeder roots (to increase ramification) and that some (maybe all?) deciduous trees will just remain in hyper tufa pots or go into wooden boxes. My thinking with the deciduous trees is that I want to grow all aspects of the tree at once (in other words, branch structure, root ramification, trunk size etc) which is admittedly slow but the tree will look beautiful while they’re growing so I can keep them in nice pots close to the house. For the flats and bags I’m going to put them in a sunny spot to grow but not have them on display (if you will) near the house.
So which method works best for what? Conifers in grow bags? Deciduous in boxes? Broadleaf evergreens in…? Everything in Anderson flats?

I think they are all valid for prebonsai. Clearly the growbags are the only option if you want to put them in the ground too. Anderson flats can be placed on the ground to let the roots escape into the ground but you’ll want to pick them up and trim them back at least once a year.

After that the main benefit of a growbox over Anderson flat is the size. A wooden growbox can be made into an appropriate size and depth for a specific tree. Sometimes Anderson flats are too big for a tree and the tree will do better in a small container. I know some people will sometimes section off an Anderson flat and grow two or four smaller trees at a time in one Anderson flat if that’s appropriate.

I’m not familiar with hypertufa but it looks like another training put but with less bottom aeration. If the size is appropriate it looks like an okay choice but probably better suited more for secondary /refinement than trunk development.

If you are not careful the conifers will get leggy and it may hard to get back budding. Most deciduous trees will back bud quite well, even from the trunk so they can get leggy and then be cut back hard if your goal is a thick trunk. In either case, getting a good nebari started in a fairly shallow pot is well worth the effort in my opinion. Giving up a couple of years of strong growth to get good roots is a good trade.

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Ahh. That’s a great point. You can make smaller sized wooden boxes. What have people used to separate deeps? Also what’s an appropriate size for a custom box? A few inches on each side bigger than the root mass in general?

If I’m not careful meaning that if I don’t prune them back and/or plan out some sacrifice branches? Is that what you mean?

Usually a wooden divider is enough to create compartments in an Anderson flat. Some long roots may escape around the boards but they should be easy to control with root pruning.

As for appropriate sizes, I think a couple inches larger than the rootball is good for boxes where you are trying to grow the tree still. You could go a little bigger but you have to be careful about watering until roots occupy the edges. If you go smaller you probably won’t get the growth you are trying to achieve.

I’m going to throw another way of growing just to help. I use air pots for everything, conifers, deciduous and broadleaf evergreen. They get really fantastic root bases (including good nebari) and the growth is fantastic. In a good year you can the equivalent of two years growth. The down side is you still have to water them.

You need a combination of sacrifice branches to get them to thicken and pruned branches to maintain foliage close to the trunk. My experience is that this is easier to do in a grow box than in the ground although the growth rate is not as fast. However, there are those that do the combination very well in the ground, normally in grow bags. I am working on that.

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This is great information. Thank you!