I take all of my more established deciduous shohin trees out of their pots each spring, not necessarily because they need to be re-potted but mainly to check the condition of the soil and roots. I find that the top centimetre of soil in the pot breaks down quite quickly in our climate, and retains too much moisture. This does nothing for the tree, but does provide the ideal conditions for mosses, liverworts and insect larvae. I clean the decayed soil off, trim the roots if necessary and replace the tree in it’s pot with some fresh akadama and kiryu.
Here are some pictures of the trees that were re-potted today
This cork barked elm needed the roots trimmed a little
The roots on this trident were OK but the top layer of soil needed to be replaced
Cleaned up and ready to go back in the pot
This Shishishigira got the same treatment as the trident
Potted up and good to go for another year