As an experiment to test the viability of repotting in the summer, when leaves aren’t growing, and roots are, I repotted a Japanese Black Pine, and a Japanese Maple. The pine had been in that pot for a few years, and was building a good head of steam. It did not need to be repotted this year, much less in the summer. The Japanese Maple had been repotted this spring, aggressively root-pruned, and I was surprised how little the roots had grown when I unpotted it.
Just for an added degree of difficulty, here is the almanac of weather for the next couple months following the repotting, done on 8/11/19. Nearly every day was over 90 degrees, all the way until 10/5/19; 55 days over 90, 7 days in the 80s, and even a couple days over 100.
One month later, 9/15/19:
Two months later, 10/6/19:
It’s looking pale, but the buds are still doing ok. Here is a comparison of this pine next to another JBP:
4 months later, December 22…winter hue, or trouble? We have had several nights down in the mid-20s f, and none of the pines received protection.
Mid-March 2020. I’m reasonably confident the tree will live. Buds are swelling, but the color is pale:
Compared to another JBP from the same batch of seeds:
Late May, 2020. The dominant candle has failed, and a few other candles are opening.
Compared to the JBP from the same batch of seeds, which was dug from the ground this spring, and essentially bare-rooted. It is clear to me that March is a safer and healthier time to repot JBP:
Likewise, a Japanese Maple which also didn’t need to be repotted, and was, in fact repotted earlier in the spring of 2019:
Root pruned:
Wired in:
Watered in, 8/11/19:
8/18/19:
8/25/19:
9/1/19:
9/8/19:
9/15/19:
9/22/19:
10/6/19:
10/27, new growth is promising:
December 1, After leaf-fall:
In Mid-March 2020, after spending all winter on the bench with other J Maples, I was a bit surprised to find this tree was dead…
…wait…
4/1/20:
Late May, 2020. A few shoots have emerged from the trunk. The top half of the trunk is dead, so I lost 2 sections of trunk which had taper and movement.
Conclusion: I will not be doing August repotting again.
Nebari Bonsai 
excellent blog……………as usual!