Rootbound

From BonsaiWIKI

You can usually pop the tree out of its bonsai container and check out the roots. Some adventurous roots trying to escape the pot is not usually a problem. You can clip them away to keep the drainage holes clear and wait for dormancy.

You know your plant is rootbound when:

1. the bonsai soil is not draining well and you have difficulty keeping the bonsai soil evenly moist
2. the plant is suffering in some way
3. when you examine the roots you see several spirals of roots encircling the container or notice the plant edging up out of the pot like a cobra ready to strike. Then you need to take some action, that might include emergency repotting.