Imported trees to the US are bare-rooted- pines and all. You can bare-root Pines, however the odds of a bad outcome are orders of magnitude greater than if the tree is handled more carefully with a "sectional" barer-ooting, where the roots are cleared of old soil 1/4-1/2 of the tree at a time. I bare root young, rapidly growing pines frequently, to get them out of organic based commercial growing medium, after they have been dug, collected, etc. You need to protect them, keep them appropriately hydrated and not be surprised when once in a great while you lose one. A lot is determined by how strong and healthy the tree is before you change it out, old, perhaps slowed bonsai, I would think long and hard about. I would also suggest that you work with someone who has done this before, if you decide that you must try bare-rooting pines.

Chris Johnston wrote a little article that showed how we bare-rooted a fairly large and cumbersome Ponderosa Pine that had been collected a number of years earlier and left in its duff, it was given to me by the collector, it is now thriving (my wife and I just lifted it on to a winter storage bench last weekend. Note While we rinsed the roots gently, did not power wash or use a high pressure nozzle like we might have with tridents or other farm grown deciduous trees.

http://bonsaikc.com/advanced-techniques/dealing-with-difficult-roots/

It is easy- don't touch the bark. Period. John

Hmmm ... maybe I know now why I lost a Scots pine this spring.

John, I got the tree from Meehan's in August '09. It went thru two winters in good health. I repotted it in early April; the candles were elongating, but not starting to open yet. I put it into a 3:2:1 mix of scoria, bark and Turface.

I did bare-root it, to get all of Meehan's old mix off. (There was a distinct difference in particle size; my mix was coarser, overall.) I tried to be gentle with the roots, but may not have been as gentle as needed.

I gave it good aftercare, I believe: partial shade, misting, extra care in watering. It looked OK for a month or so, but growth never resumed, and the foliage eventually began to die. From there it was all downhill.

I've been at a loss to explain why it died. One possibility I considered was that I had left voids in the mix that let roots dry out. But from what has been said here, I wonder if I simply manhandled the roots too much.

Thoughts?