Best method for developing Nebari on nursery stock in the field

[BirdsBBQBonsai]

I have over 100 plants in 3-5 gallon nursery containers that I want to put in the field to develop nebari and trunk. What method will give me the best results? Tourniquet ground layer? Should I bury in a grow bag in the ground or just the ground? Can nebari develop if still in the nursery container on the ground if I let roots escape the container to go into the field soil? My goal is elite level nebari no matter how long it takes. I'm in zone 6. Thanks!

 

[Glaucus]

You should set up the nebari roots in a pot before you plant it in the field. The field is only to thicken it up. Then, there is a technique where you dig up the tree after a few years, you bare root just the top roots, fill it in with substrate, and then you plant it back. And then 1 or 3 years later, you dig up the tree again, cut off everything that is not in the bare rooted/substrate part, and then you put it in a training container. This technique is not so much to develop the nebari better, but to transition from the full ground and soil to a container with substrate, easier.

Things depend on species, but the first rule of ground growing is to first set up the nebari and the movement in the trunk. Once you put it in the ground, it is just going to grow and try to become a tree, not a bonsai, assuming it is a true tree species and not a shrub.

And a grow bag is probably a must for any field growing. Also makes it much easier to get the tree out of the ground. Growing shohin in the field is a bit silly. And for larger bonsai, digging up such a tree is often a 2 person job. Getting all the long roots and sever them may be a pain for many species.

 

[Shibui]

I also develop good starting nebari before committing the trees to the grow beds.
Layering in the grow beds can work but not infallible. Intermittent watering can allow new developing layer roots to die or not develop properly leading to uneven nebari. Planting maples too deep will induce then to develop new roots just under the surface and your layered nebari becomes redundant.
I prefer regular dig and root prune to grow bags because it gives me the chance to check and adjust nebari as it develops. I can also encourage better root ramification closer to the trunk. Root bags only seem to cause roots to ramify closer to the bag walls.
Bags also don't stop roots growing down which discourages trunk base flare.

I have no problem digging trees when roots have not grown too thick. Regular dig and replant helps keep lateral roots thin and down roots to a minimum making digging much easier.

Planting nursery pots in the ground may give variable results. Whichever root escapes first will become the thickest, leading to uneven nebari or, if a down root escapes, very little nebari and trunk base flare.