First things first you should have everything you need at hand before starting. There's nothing worse then having a tree out of the pot and not finding your screen for the holes, or that your don't have enough soil mix, etc..
The tree we're going to work on today is a San Jose Juniper then I've been working on for about 7-8 years from a 15 gallon sized plant. It's been repotted a number of times so it has a good root system. Here it is before any work.
Bend to form a S shape.
I use a repotting sickle to loosen the tree from the sides of the pot.
If I were using the same pot I would remove the tree and cover the roots with wet towels while preparing the pot.
After cleaning the top I start to gently comb out the sides of the rootball then the bottom. As you can see there are lots of nice healthy roots hanging from the sides but not too many straight down from the bottom.
As you can see the new pot is considerably shallower then the old one.
Then I remove the tree, put a layer of soil in the bottom of the pot and a mound in the center. The reason for the mound is that there is a little depression right under the trunk from removing the old nursery soil.
Even though we screen the soil when we make itI like to screen one more time just before I use it.
Next I check it's position in the pot making sure it is the way I want it to be.
Always make sure that each wire is tied to itself not the other wire. This way when you pull the slack out you are tightening the wire. I take the long end of a wire , bring it across the front of the rootball and tie it to the short end of the same wire.
Then I do the same thing on the opposite side. I pull the slack out of the wires relax the pressure a bit a twist them together until tight. Releasing the pressure when twisting lessens the chance of breaking the wire .
Then take those two wires pull them across the rootball and tie to each other.
Now add soil and work in with a chop stick being sure to fill any voids.
After the soil is worked in finish by going around the edges with a trowel is insure there is a lip to catch the water all around the pot. If there is no lip because of too much soil a lot of water just runs over the edge.
There should be absolutely no movement if the tying was done correctly.
Now water thoroughly including the foliage. Water until the water is coming out of the bottom of the pot, clear, as fast as you're putting it in. When the water is clear it means any leftover dust is flushed out.
And that is how you repot a bonsai.
A word about soil mixes- there are a jillion mixes used for bonsai. Everyone has to find their favorite based on local product availability, need for water retention or drainage and a bunch of other factors. For me on my conifer bonsai I use the following- 1 part small akadama, 1 part large akadama, 2 parts lava rock and two parts washed pumice- this works for me very well.
Here is the tree after it's haircut and repotting.
I hope that you all find this post useful. As always I welcome any comments or suggestions for future posts. Until next time.....