Developing Nebari on Nursery Stock

[Tntthunder]

So I have a few trees (Chinese Junipers) now, all bought from a normal garden nursery, put good random bends in the trunks, wired the branches into decent directions and they seem to have survived the harsh Finnish winter on my open, unprotected balcony. (Not sure yet, they're still green though so that's good I guess?)

Now I plan to let them grow for a few years and do their own thing to help them thicken up only trimming them enough to stop branches being shaded out and allow air flow. Along with slip potting them into bigger pots when needed.

However in this development stage I am constantly seeing people say "develop the nebari, do it when they're young or you will have to rework them".

So my question is how do I develop the nebari? Especially on a tree that has been in a nursery pot (it's about 3-4 years old) with no work done to it. Also how do I develop the nebari whilst also trying to thicken them in a pot? How do I encourage them to grow thick and radial?

Haven't really be able to find detailed explanations or guides/techniques to help with this particular aspect. If they were cuttings I could place their roots but how does it work for garden nursery stock with roots in their place already?

 

[Wires_Guy_wires]

Junipers produce roots all around their trunk when they're in a pot. So this is one of those cases that, to me at least, seems like an exception.
You can encourage the "foot" to widen by cutting off downwards growing roots and keeping the ones that come off the trunk at soil level.
They will develop along with the trunk itself.

 

[Shibui]

First up, juniper bonsai are not noted for extensive nebari. I guess that's related to the rocky mountain soils they naturally grow in rather than deep fertile soils of the valleys. I therefore don't get too worried about nebari on juniper. More is good but uneven or less visible roots is OK too.

My Chinese junipers voluntarily develop new roots at soil level (sometimes even a bit above soil level if there's enough humidity under the dense branches) so you can expect your trees to add extra roots while they grow in the ground.
@Wires_Guy_wires advice re pruning any down roots and leaving horizontal roots is exactly the way I root prune before planting trees in the grow beds here.

I would expect the nursery stock to be cutting grown so it is likely you'll find the roots from the trunk are reasonably radial. Depending how ling they've been in the pots you may just be able to pull the root ball open into a reasonably flat arrangement with a little cutting here and there. If you need to cut or rake a bit more then do so but bear in mind that junipers do not like radical root reduction. Each tree is likely to be different so hard to give blanket advice that covers all possibilities.