I live in zone 5 in the States. I have plenty of room to put trees in the ground to grow out. I do have some tree ideas that would not survive a cold zone 5 winter. That's my background.
I have 2 questions... Should the trees that wouldn't survive a winter here be automatically put in a grow box and just moved for wintering or is the planting in the ground so advantageous that I move them out of the ground to my cold room every season?

2nd question...For the trees that would survive the winter that I could leave in the ground...what have you found to be the best ways to promote the finer root growth necessary for the future tree? I've read a few things, but I'm curious what some of you on here are doing...real world results. Thanks

If you have been reading a lot you must have noticed that putting trees in the ground means they are not lifted for several years. As you would have to lift them every year, there is absolutely no way you are going to get good growth in the full ground. Put them in boxed.

I am not sure what you mean with promoting finer root growth? I just avoid getting the main roots to heavy, by lifting threes every few years and to a maintenance prune on the big ones. There are plenty of guides out there and everyone has their own strategy.

Thanks. You answered my question without knowing it. I have read a lot, but by you telling me that you personally lift a tree out of the ground every "few years" gives me a time table. This also gives me a person to question vs an article to read...
Do you plant your trees over a tile or any obstruction like I have read? I've read this promotes a shallower root system. Thx

of course