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I have a Chinese Elm bonsai. The tree was doing fine, sprouting many new twigs in the last month or two. After the growth slowed down I decided to repot the tree, because the original soil was too slow to dry out and also because the roots were starting to fill the pot.

  • I used something called Terramol as the substrate, it’s supposed to be something like Akadama. I didn’t mix it with anything. (The supplier says it can be used as is.)

  • I had to trim some of the roots so that the plant would fit neatly in the pot. I was very careful doing it, only trimming a small part of the roots.

  • I think my watering routine should be fine – I always water after the top part of the substrate gets sort of dry, and I keep pouring until the water comes out through the drain holes.

But after a week the tree looks tired and wilted, some of the leaves are turning yellow. Is this expected after repotting, or have I done something wrong? If I screwed up, what’s the best way to help the tree?

This is how the tree looks now, after repotting once more into a mix of Terramol (two parts) with grit (one part) and potting soil (one part):

Bonsai Elm tree after repotting

And this is a detail of the pot & substrate mixture:

Pot and substrate

Update: After a month or so after repotting the yellowing stopped and the plant started to look happy again. This is how the tree looks today:

Happy tree

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I don't know where to start.

Do you use this as an indoor Bonsai? Where do you live? First of all you can't use that substrate if you don't use a special fertilizer. Then you can't cut the roots of a tree when it should have a winter break. And after that put him into literally rocks and water.

You need to put that tree into your garden, bury it so the trunk is covered by earth at least 10 cm. Let it stay there until mid of April. Use the time to get informed about how to treat a Bonsai tree the right way. Then buy real Bonsai substrate or learn how to mix it. If the roots don't fit the pot after you cut them the right way, buy a new pot that fits. Elm trees are famous for taproots, so I doubt a plate is the right thing to use without experienced treatment. Put the tree into a place where it can have morning sun until midday and then is protected from too much sun. Make sure it only gets much water when it has a good ventilation or it easily dries out.

There are many Howtos to find for Chinese Elm Bonsai, they will help you from here.

Good luck!

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  • Thank you! This is an indoor bonsai; I live in the Czech Republic. The plate is just an illustration to describe the substrate, I have a regular (deeper) pot for the plant. I have read what I could before repotting, and most of the sources recommended March as a decent time to repot…? Also, the substrate was described as especially suited for bonsai trees, just as Akadama, so what’s a “real bonsai substrate” if not this?
    – zoul
    Mar 15, 2013 at 13:21
  • Well this substrate is like stone wool used in hydroponic gardening, all the small roots of the plants get into the cavernous stones with myriads of holes. But you have just cut his roots and therefor stripped him off of all the small roots, and put him into a substrate that only works for small roots. That doesn't work. Cutting roots for Chinese Elm should be done 1 month before spring, we got still snow in Western Germany, I guess you are 2 months away from spring in Czech Republic. Don't put him outside if you use him as indoor Bonsai.
    – Pachty
    Mar 15, 2013 at 14:06
  • I only trimmed the roots, ⅓ at maximum. Do you think I should repot the tree into a more traditional substrate? I’d hate to further disturb the plant unless the change is guaranteed to make it better. (The spring is almost here, the outside temperatures will raise to 10°C in a few days. The tree stays inside.)
    – zoul
    Mar 15, 2013 at 14:12
  • This is just a suggestion what I would do, I cannot guarantee it is correct. Take the tree out, remove one third of the substrate and add sand + turf in a ratio of 2:1, mix it and put the tree back. Don't use too much water now.
    – Pachty
    Mar 15, 2013 at 14:23
  • I’ll try. Will report back when the outcome is obvious. Thank you very much!
    – zoul
    Mar 15, 2013 at 14:25
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When you say used it as a substrate, is that all you have in there? A bonsai is not going to survive off just water, so you can't have just rocks and water.

One of the most important things to know about bonsai is not to do more than one major thing at a time e.g.

  • don't heavy prune the roots and heavy prune the branches
  • don't change the soil mix and heavy prune the roots
  • don't significantly reduce the amount of soil and prune

I just read that you are in the northern hemisphere, I would suggest that March is too late in the season to prune and repot. I would suggest early winter. If you trim too close to spring you run the risk of the plant going into shock and missing out on your prime growth period.

My advice would be to return it to its original pot and tackle this again next winter after your plant has recovered. I think it is not happy where it is and you risk losing it.

If you are having problem with too much moisture, I typically put crushed tiles or anything clay like in the bottom of the bottom to allow free drainage. In your case, maybe you could put an inch layer of Terramol since you have it available.

I would ideally like to see pictures of the pot you have it in, but if it is anything like the picture provided you are going to have some problems because there is little space for soil / roots / substrate. People get confused when they see pictures of bonsai and it looks like a massive tree growing in 3 inches of soil. Plants can't just go from a deep pot to a saucer overnight.

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  • Thank you! See the previous answer, I have now repotted the tree once more into a mix of Terramol (2 parts) with grit (1 part) and regular potting soil (1 part). Obviously I plan to fertilize later, when the plant has recovered from the repotting. As for the pot, again, the “plate” picture is just an illustration, I have a regular bonsai pot several cm deep. (The tree used to live in it and was happy.) And as I wrote above, I’d hate to disturb the tree yet again unless it’s emergency and guaranteed to work. What do you think?
    – zoul
    Mar 22, 2013 at 7:47
  • @zoul - It's looking happy. With the new mix in place how is the drainage working out?
    – going
    Mar 24, 2013 at 22:46
  • The drainage is perfect, as far as I can tell. The water gets in easily, gets out easily, stays for a day or two, no “swamping”. The tree is still wilted and I got more yellow & even dry leaves since the second repotting a week ago, it’s hard to say if it’s slowly getting better or slowly deteoriating even more. I guess I’ll mist & wait, have no idea of anything better to do.
    – zoul
    Mar 25, 2013 at 7:11
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I don't think there's anything wrong with your original 'soil' mix, provided it was screened properly - several of my plants are in a pure inorganic mix and are quite healthy. I also know a bonsai nursery owner who successfully grows everything in a pure inorganic mix.

In my experience, a plant will grow in a pure inorganic mix with only water for quite a while before fertilizer has to be added.

I suspect that the yellowing (and drying) is being caused by too many feeder roots being cut during the root pruning - meaning that even if you water properly, the remaining roots can't absorb enough water to support all the foliage.

If all the roots were trimmed by 1/3, without consideration for what was being cut, it's likely you took too many feeder roots (only the feeder roots -the small, white, hair-like ones- absorb water and nutrients; the heavier roots are just for transport and anchorage).

I would leave it in the soil it's now in (re-repotted) and reduce the foliage a bit.

Also, give it some SuperThrive when you water and mist the foliage with SuperThrive between waterings. The SuperThrive will help the tree put out new feeder roots and restore the balance between roots and foliage.

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  • Agreed. The soil seems to work fine now and one bonsai master I consulted said I should have reduced the foliage after pruning the roots, because the remaining roots were too few to support all the leaves. Now, about two months after repotting, the tree looks happy again; see the last photo in the question. Thanks!
    – zoul
    Jun 22, 2013 at 18:02
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I know the question has been answered but i thought i would add to this with my experiences with the same issue.

Its good to see your tree bounced back,

In our nursery we had the same issue with a few of our trees, and for weeks scratched our heads, until i started to notice a pattern.

We employed a new member of staff, which was re-potting a few of our trees and it seemed it was some of the trees they re-potted was the trees that was looking sorry for themselves.

After further investigation i found that there was the smallest of air pockets in the pots, I honestly wouldn't of thought it would affect a tree that quick.

We re-potted the trees as soon as possible and all trees bounced back.

Many people might disagree with me but we did not feed the trees in question until the next growing season, and kept carefully watering them.

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This plant's roots are exposed and it will die. It's suffering shock. Replant in a deeper container and add rich potting soil. Put in sunlight in days and water a couple times a week.

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