Repotting demonstration: Japanese Maple

Welcome to spring 2014!  I imagine at this point most of the people who read this blog have either finished up their repotting for the season or are close to it.  My original plan was to get this article up a couple of weeks earlier but things just didn’t work out that way.  Better late than never.

In this article we will look at the play-by-play of a repot job on one of Aichien’s Japanese Maples.  This tree is still very much in the development phase, so I thought it would be a good tree for an article.  I’m sure many people who are interested in reading a repot demo probably have plenty of trees in this phase.  This is a nice place to start focusing on good root set up to ensure we get things growing in the right direction.

Lets take a look at the tree.



When this tree made the transition to a bonsai pot the branches had to be cut back to a location closer to the trunk and the roots got cut back closer to the base.  Before being cut, the lower branches received approach grafts to get new growth close to the trunk before removing the bulk of the branches.

close up of the graft areas.

close up of the graft areas.

The above photo shows the graft unions and it’s easy to see the path of the branch and where both the approach branch and large branch where cut.  Later in the growing season I’ll clean these cuts up again to get them started in the healing process.

First things first let’s get the pot off of these roots.  After cutting the tie down wires start digging the tree out of the pot.  Use whatever gets the job done for you.  The industry standard tool for this job is one of these Japanese sickle knives.  They are available at most bonsai supply retailers for a relatively reasonable price.  Or if you happen to be in Japan you can pick one up at the 100 Yen shop ($1 shop).  I like that price better!


Dig a trench around the lip to free the roots from the inside wall of the pot.

If all goes well the pot should pop off cleanly and easily.  PotRemoval

Once the pot is off its time to dig.  Wait a minute!  Set the pot up first.  No need to make the tree wait for the pot to get set up after we take off the soil and cut the roots.  Best to do it now, then we’ll start digging.



Set the pot up in a way that is effective.  You can use all types of fancy wire tricks to secure the drain hole screen.  However, nothing more than this simple staple style is necessary.  Copper wire is expensive and really hard on the roots, so its best to use something else.  Aluminum is good for this job.  At Aichien, we use a steel wire with a colored coating on it.  We change the color each year to help keep track of when the tree was last repotted.  One is just as good as the other.  Your choice.

Time to dig!


I like to start from the bottom and work my way up.  Using this modified hand rake (also from the 100 yen shop) we can gently break the root ball up and knock the soil loose from the roots.


With the soil knocked off there is a good view of what type of roots the tree is working with.  There are a lot of roots growing directly under the trunk.  Those roots are un-necessary and also make it hard to keep the tree in a shallow pot.  Especially if they keep growing and get stronger/thicker.  Fortunately there are also a lot of roots growing around the outside edge of the root ball.  So cutting these roots down to the bottom of the trunk will be no problem.


start cutting

then cut more

then cut more

getting close

getting close

With the roots cut close to the bottom of the trunk we can see some odd root formations, knobs and bumps.  Flat is better.  So let’s cut those down using the concave cutters.

cut3 CutFlat

Now that the bottom is cut flat and all of the roots directly under the trunk are gone it’s time to start working the top of the root ball.


With the tree back in the upright position I like to scrape the surface soil in a downward motion moving from the base of the trunk to the edge of the root ball.  This is a gentle process.  The goal here is to knock off the old soil and we are also combing the roots out by doing this.  The ideal image i keep in my mind for how these roots should look is like a bicycle wheel.  Think of the hub as the trunk and the spokes as the roots.  Everything growing in its proper position, evenly spaced out and not crossing over one another.


here is a closer view of the beginning of the scraping process. Take off all of the moss and really get in there to see what’s been growing.


cleaned up, combed out and ready to start making some more cuts.

Once everything is cleaned up and combed out we can start to make some decisions about what needs to be cut off.

Stacked roots are un-necessary.  So we can always plan to cut off at least one root from areas where they are stacked on top of each other.  Use your best judgment when it comes to choosing bottom root or top root in this situation.  It’s a case by case decision.  Roots that are growing in a high position on the large surface root are not needed either.  We want to get the roots to appear as though they are all growing from the same horizontal line around the trunk.  The photos below show a root that is both stacked and high on the surface root.  Let’s cut it off.  Look for this pattern all around the trunk and act accordingly to help develop a nice clean line where the soil meets the roots.




Another example of an out-of-place root. Cut it off.

This tree has an area in the back that is fairly weak.  Nothing will be cut here.  Just let it keep growing.  It will catch up with the others eventually.  This area will be re-evaluated at the next re-pot.  If need be we will graft new roots into this area.


weak root growth

Before finishing up the root work we can cut nice clean circle around the edge of the root line to get everything at an equal length.

Here is a view of the bottom of the root ball after all of the root work has been done.  It’s easy to see the weak areas and strong areas.  The ultimate goal is to even all of this out to a more solid circle. By repeating this root work every year or two, the gaps will begin to fill in.


Before putting the tree in the pot a base layer of soil is laid in with a good size mound in the center.  As the tree gets worked into the soil that mound will flatten out and push to the sides, leaving a tightly packed and stable base directly under the trunk.  For deeper pots and conifers we can use a drainage layer of large pumice or lava or something like that.  In this case, it’s not needed.  It will already be difficult to keep this tree from drying out due to the shallow pot and well draining soil.  No reason to help it dry out any faster.



base soil and mound

I’ll save the soil preference for another post. This mix is mostly fired red clay, pumice and a little gravel.

When the tree goes in, it’s good to twist it back and forth to sink it down into the new soil.  Then step back and take a look to make sure everything is centered.  Check the side view as well as well as the front and the top view.

centered in the pot

centered in the pot


Top view. Centered in the pot.

Once the tree is in a good position let’s tie it down.


tying in

There are a few ways to lock the tree into the pot.  Whatever works for you, is best.  Tight and secure is the way it should feel if tied in properly.

nice and tight.

nice and tight.

Tied in tight with the wire arranged in a way that will allow it to be hidden by the next layer of soil.  I like a nice clean look with no wire showing, but it doesn’t really matter if the wire shows.  Again, personal preference here.  Moss covers it all up at show time and if it won’t be shown it’s a non-issue.  The tree doesn’t know the difference.

Next step is a second layer of soil.

Adding more soil.

Adding more soil.

When adding the second layer I like to fill the pot a little bit higher than the lip at first so there is some extra soil that can be worked down into the gaps.

Use 2!

Use 2 chopsticks!

This step seems to be universal in the bonsai world.  Chopsticks are one of the best tools available to push soil down into the gaps between the roots.  I often see people doing this with just one.  Use 2! it does a better job.  No need to get wild with this step and smash up a bunch of soil.  Gently pack the soil in until it begins to feel firm, then move to the next area.  I like to start at the front and work my way around counter-clockwise until I get back to the front.  You can try different things out and see what works.

all done!

all done!

Once the soil is packed in nicely we can smooth out the surface and give it a pat to lock everything in place.  If we do a good job with the chopsticks and surface pat, the soil won’t move when we water.  No need to break out that funny little bonsai trowel thing and pretend to set the edge.

hose it down!

hose it down!

This job is done!  It’s back to the bench for watering and we can move on to the next tree.

As always, thanks for reading!

Until next time…