Sidesummy's JBP & JRP Ground Growing Progression

[Sidesummy]

I have done something similar to Option 2 above with a shovel to slice through the ground/roots around the trees. However my trees (JBP) were only planted 2 years prior, so the roots presumably weren't as thick/advanced as what I am imagining you will have. The results were good. I left them for a further 12 months and successfully transitioned them from the ground into shallow plastic training pots with a nice amount of finer roots close into the trunk. I didn't lose any trees in this process. I feel you might have a potential issue with thicker roots extending out quite a way before the finer feeder roots emerge from them. The only way to resolve that is to cut back so I think any plan to reduce the root ball while they are still in the ground is better than nothing. Healthy fine roots close to the trunk/nebari are key to giving the trees a solid future as bonsai. I absolutely think there is a good chance you can still achieve that ... good luck with them!

Any suggestions on timing from your experience? I had though early spring made the most sense to me. But here's some of my rational:

-Early Spring when buds begin to swell? This would be similar to a repot I suppose where root work is being done and roots are being cut.
-Middle of the growing season? Tree is vigorously growing, might be able to send out new roots easily because everything is growing right, why not the roots too?
-Autumn after needles have hardened for the season? Seems like the worst possible time if the tree has sent all it's resources back towards the roots for safe keeping during the winter. Probably shouldn't go cutting them at this time as I feel it would weaken the tree for the next season.

I guess I just feel torn, should I do it in spring or in the middle of the growing season.

 

[Ryceman3]

Ideal timing would be when you usually root prune. For me this is mid/late July (as things begin to move after winter) and that is when I did the shovel work. The other time I would consider it is early autumn, because in my climate there is plenty of time for new roots to grow and strengthen before winter (which is pretty mild for me anyway). Being from Australia, I don't really understand/relate to the USDA zoning, but I am guessing Zone 6a is a fair bit different to 9, so you would need to take this into consideration and use your own judgement. In the middle of the growing season, I can expect temperatures of 40degC (104F) so I wouldn't be overly keen to cut pine roots then, but this may not be the case for you...