Repotting our trees is a key bonsai practice, and one that you must gain mastery of. Here is a summary of basic steps you’ll take each time you repot your trees:

  • Make sure you have all necessary tools and supplies, including prepared soil, before you start
  • Have a suitable space to work in – outdoors a bench is ideal, indoors a small bench or table and a large tub to work in will help keep the mess contained
  • Prepare the new pot if you’re changing pots; if not, you’ll need to thoroughly clean the existing pot, replace drainage screen and the tiedown(s)
  • Unpot the tree and inspect the root mass
  • Comb out the roots which will have coiled their way around the outer edges of the mass
  • Trim away the overlong roots and enough of the root mass to give room for fresh roots to grow
  • Make needed corrections to the roots, namely the exposed nebari roots that are part of your design
  • Add fresh soil to the pot to provide a thin bottom layer – slightly heaped in the middle
  • Place the tree in the pot
  • Tie the tree down once you’re satisfied with the placement
  • Fill in all around the tree and any spaces in the root mass; use a chopstick or other tool to work the soil in
  • Water thoroughly; allow to drain; water thoroughly a second time; newly potted or repotted trees with fresh soil will need to be watered more frequently than others, as it take a while for the fresh soil to become properly wetted
  • Fertilize (this is optional at this time, but I tend to forget as I move on to other trees, so I go ahead and do it at the time of repotting)
  • Place moss on the surface if so desired.

This is today’s subject, the Chinese elm that has its own Progression page.

It was last repotted in 2018, and though it could probably go another year without it, there are a couple of issues with the nebari that I want to correct before they get out of hand.

This is one of the roots that I’m unhappy with. Though it’s grown well and is about healed from the previous pruning I did, it’s just too straight and untapering a surface root to remain. I can solve this problem as part of the repotting process.

This one’s a little harder to see, but the surface root at the left has a smaller root coming off it that runs at an angle back toward the base of the tree. It’s also too long without taper and needs pruning back.
Step number one, the tree is pulled from the pot. It’s at this point that you do the assessment of the root mass. Look for any root rot caused by poorly draining soil. Always cut away any dead roots – you can’t eliminate all the fungal pathogens by doing this, but removing the dead roots and using free-draining soil when you repot will allow the tree to recover on its own (which it should do). Expect to see fresh white feeder roots when you inspect the root mass. This is a good sign, of course. Don’t worry about trimming these off as a necessary part of pruning the roots to make the mass more compact; the tree will happily grow new ones.

I combed out the root mass, trimmed away some of the excess roots, and washed off the excess soil that I’ll be replacing. It’s easier to see root problems once you get to this stage. In this case, it’s a root that’s coiling back toward the trunk base. These should either be removed entirely, or if you need a root that’s grown this way then gently uncoil and trim it so it grows in the desired direction.

Here I’ve pruned that first of my large offending surface roots. I’ve also removed the coiling root that I don’t need since I have a good mass of roots to support the tree.
In this photo you can see that I’ve pruned back the large root even more. My goal is to build the taper of this surface root. By pruning it back, I can expect the roots already branching off this one to continue to thicken over time. That should produce the effect I want.
Here’s the view from the other spot where I have that odd root moving back toward the trunk. There’s obviously work that needs doing.
The offending root is gone, and I’ve pruned back the too-straight surface root as I did the other one. I’ll be able to build taper with this one as well.

Here’s the tree after the final root trim. I’ve removed about a third of the total root mass, which is the right amount for this repotting. The amount of root mass you remove will vary based on how long it’s been since the last repotting, and how much root the tree has grown in the interim. With experience you’ll be able to immediately gauge this as soon as you pull the tree from the pot.

Here I’ve placed the tree back in its pot. I previously washed the pot thoroughly, made sure the drain screens were in good shape, and replaced the tiedown wire.

Placing your tree in its bonsai pot requires you to consider several parameters to ensure the composition is its best. They are (in no particular order):

  • Determine the correct placement of the trunk base – in this case, since my tree emerges straight from the soil and terminates left of center at the apex, the base needs to sit slightly toward the right side of the (oval) pot
  • The tree also needs to sit slightly to the rear of the pot
  • The tree sits on a slightly heaped mound of soil, which brings the base just above the rim of the pot
  • I had previously selected this pot because it is, in profile, roughly as deep as the trunk base is wide
  • The pot measures about one-half the height of the tree in length, making for a good proportion
  • The initial portion of the trunk emerges straight from the soil; the planting angle needs to be such that the initial portion of the trunk is perpendicular to the pot rim.
The tree has been tied down (I use a single tiedown for most of my bonsai; use however many work best for you), and the pot filled with soil. This step requires a lot of care. You can’t leave any gaps beneath the surface of the soil, because that spot will dry out and any roots there will die. Most everyone uses a chopstick to work the soil into and around the root mass. Some will say never to jab the chopstick into the root zone when you do this; I’ve never found this to cause a problem, since there really aren’t that many tender roots present at this stage of the process. If you’re concerned, then you can carefully insert your chopstick and wiggle it back and forth to work the soil in.
Here’s a closer look at the nebari. I’ve improved the surface rootage quite a bit, and this should result in a much better bonsai in a fairly short time. This tree has been in training since 2014, so the next few years should complete the making of this Chinese elm bonsai.

The final presentation for today. I did a little trimming of the branches (there’s probably a little more to be done), then watered and placed some moss on the surface. I also added some time-release fertilizer so I don’t get busy with other trees and forget. Because I’ve done root work on this tree today, it’s probably going to start opening buds within the next week. I have a lot of small Chinese elms in gallon pots, and most of them area already leafing out. Spring is getting closer by the day!

Let me know what you think of this repotting job.