Key to healthy bonsai is a healthy rootball. In summer there are things we can do without repotting that aid the rootball. If your pot looks green and overgrown, if you have decaying fertilizer all over the pot, consider practicing Soji, the Japanese technique of cleanup, applied to the pots of our bonsai.
Removing the surface coat helps aeration, it helps water penetration and aids in healthy roots for the rest of the year.