Repotting should only be attempted during the dormant season. The cut roots will heal over when the tree wakes up in the spring time so the closer to spring it is the less time the open cuts will sit in the dirt unhealed, reducing the risk of root disease. Also using a sharp root cutting tool  will make clean cuts and speed the healing process. 

 Some signs that a tree needs to be repotted are:

A: Roots appear near the edges of the pot.

B: Roots growing from the bottom drain hole.

C: Poor drainage or slow absorption of water.

1: Use a wire cutter to snip the wire on the bottom of the pot that secures the tree to the soil. Being careful not to cut the screen clip.

2: Cut the soil loose from the pot and carefully remove.

3: Carefully rake out and untangle the roots with a root hook. Do not disturb the soil right near the base of the trunk.

Water is good at his point as it is critical the root’s do not begin to dry out and it also loosens up the old root ball and soil.

4: Use a root cutter to remove the large woody searcher roots leaving the small delicate feeder roots. The tree at this point can be moved up to a larger pot if you would like to increase the overall size of the bonsai tree.

5: If you want to keep the overall size of the tree the same only increasing the trunk and branch thickness, cut off the feeder roots so there is about ½ “ to 1” (depending on the pot size) of space between the pot sides and the root ball.

6: Make sure the screen is clipped over the bottom drain hole and put a thin layer of gravel or coarse bonsai soil in the bottom of the pot (drainage) followed by a small mound of new bonsai soil. Set the tree into place and adjust into position. Usually a little off center and toward the rear.

7: Cut a length of copper wire and insert one end up through the drainage hole until it reaches the surface of the root ball. If you cut the wire at a sharp angle it will easily poke through the drain screen. Now bend the other end up through the other hole or on the opposite side of the screen clip wire if there is only one hole and do the same. Twist the two ends of wire together with a pair of pliers until it clamps down (not too tight) and secures the tree in the pot.

8: Add bonsai soil to the top and work it into the pot using a chop stick or pencil until you are sure there are no air pockets. Firm the soil in with your thumb until it reaches the desired height.

9: A newly potted tree should be dunked rather than watered from above as it keeps the soil from washing away.