Reducing top of Root Ball

[MrG]

Hey B Nuts,

I am pondering the recommended timing, frequency, method, etc., of reducing the top of the root ball or soil mound while a plant is in its future home pot. Some photos below to help illustrate my question.


I recently repotted both of these. In both trees’ cases, I reduced the height as much as I felt I safely could, and also changed angles, which limited the ultimate depth. I also added more bonsai soil on top than I needed to in these photos which I’ll change.

As you can see, the root mound is fairly high, so I’m wondering if I could wait a few weeks and periodically chopstick and root prune the top of the soil/root ball and redress as I go, both to lower height and to further expose the nebari.

I can’t seem to find much info on this so I appreciate any insights in advance!

All best,
MG

 

[Wires_Guy_wires]

Why is there a mound in the first place?
I think it's because there's too much soil below the rootball.
When I repot junipers, I scrape the top soil until I find a nebari and remove the bottom roots so that it will fit the pot without mounding.
If that means the bottom layer of soil I add to my pot before placing the tree in, is just one layer thick, so be it. There's good soil in the nebari already and I want the roots to grow outwards, not downwards per say. They will do that on their own eventually.

Instead of chopsticking and working the roots continuously, I prefer biting the bullet and clip the roots in the mound down to an even pane.
The longer the mound is there, the more it will be colonized by roots and the more effort it'll take to get it down to acceptable levels.

It's rarely described because in a normal repotting setting, mounding only happens when you drastically change an angle and in those cases you'd want to keep it until the roots have colonized the rest of the substrate so that there's no risk of death when you remove said mound a year or two later.

 

[leatherback]

Agreed. You have the reduction the wrong way around.
Reduce the bottom of your rootball, not the top!

 

[MrG]

Thanks for this! Definitely heard and understood.

Just to clarify, I did reduce the bottom significantly, along with the top and some on the rim (minimal), however, my focus on this repot was to remove field soil in the shin/nebari area as those were really compacted having not been dealt with prior to my ownership of these trees.

I also did change the angle on both trees which contributed to the height.

Good point about minimal substrate below - perhaps I should have lessened.

So in this case, what do you think my recourses are? Simply repot and lower from the bottom in coming years? I do personally think that the top can be worked downwards as well, and for whatever reason, I think I prefer a slightly mounded look, albeit I have them a bit too pronounced currently.

Thanks all,
MG

 

[leatherback]

You find the top of the main roots first. Then you work up from the bottom. A healthy tree can easily loos half of the rootmass, if the main top roots keep most of their feeder roots.
I find a decent assertive repot when I first get a tree helps long-term as I never have to worry about the main structure.

It is different when potting up fieldstock; I got 3 yews today, and there I am not removing a lot of the roots, as they were part of a herdge planting before and only rootsubs were left: They are in TALL containers for the first 1-3 years.

 

[Eckhoffw]

Thanks for this! Definitely heard and understood.

Just to clarify, I did reduce the bottom significantly, along with the top and some on the rim (minimal), however, my focus on this repot was to remove field soil in the shin/nebari area as those were really compacted having not been dealt with prior to my ownership of these trees.

I also did change the angle on both trees which contributed to the height.

Good point about minimal substrate below - perhaps I should have lessened.

So in this case, what do you think my recourses are? Simply repot and lower from the bottom in coming years? I do personally think that the top can be worked downwards as well, and for whatever reason, I think I prefer a slightly mounded look, albeit I have them a bit too pronounced currently.

Thanks all,
MG

Another way to say it:
You would only rake out the top mass now if the ideal surface root structure is buried.
You don’t want to be cutting a developing nebari off to reduce the mounding.

Edit: if you’re looking for a Nagari style tree -exposed roots- then yeah sure, you can tease the top soil out to show roots. I don’t think that’s what you want to do here.?

 

[MrG]

Thanks again, everyone.

Another way to say it:
You would only rake out the top mass now if the ideal surface root structure is buried.
You don’t want to be cutting a developing nebari off to reduce the mounding.

Edit: if you’re looking for a Nagari style tree -exposed roots- then yeah sure, you can tease the top soil out to show roots. I don’t think that’s what you want to do here.?

Ok gotcha, thank you. The correct answer is probably no, that I am not looking for truly exposed roots. However, I am looking to expose more of the root surface as I think I buried it or didn’t expose it enough. I’m not entirely sure as I am a relative novice in terms of experience especially. I am continually researching and a perpetual learner, so I’m not here to defend only to learn for the future. I will say I did these repots very intentionally, it just sounds like I didn’t remove enough material from the bottom ultimately.

So in you all’s opinion, what would you do here? These trees have just been repotted so I’m not sure what options I have.

All best,
MG

 

[leatherback]

Roots do not regenerate in days. So if you just repotted you could consider doing a bigger job on them.

 

[MrG]

Roots do not regenerate in days. So if you just repotted you could consider doing a bigger job on them.

Good to know. One was done yesterday and the other was done last Friday. I’m guessing both are within range to rework, you think so? Any concern of hurting the tree due to multiple traumas within days?

 

[yashu]

I’ve found there’s an exception to the general rule here (isn’t there always?). Trees started from nursery stock are generally created from cuttings (or grafts) which after rooted are often buried relatively deep in the media. As a result the roots will grow up into the soil basically creating a mat of roots well above the point that said roots grow from the trunk. You end up with the nebari buried and sometimes strangled by the plant’s own roots. In this case it seems it might be proper to excavate from the top and reduce the root ball from the top at least down to the nebari. I only mention this because many people start their bonsai journey with nursery stock and are bound to run into this occasionally. Obviously if you are working with material developed with bonsai in mind from the get go you won’t have this issue.

 

[MrG]

I’ve found there’s an exception to the general rule here (isn’t there always?). Trees started from nursery stock are generally created from cuttings (or grafts) which after rooted are often buried relatively deep in the media. As a result the roots will grow up into the soil basically creating a mat of roots well above the point that said roots grow from the trunk. You end up with the nebari buried and sometimes strangled by the plant’s own roots. In this case it seems it might be proper to excavate from the top and reduce the root ball from the top at least down to the nebari. I only mention this because many people start their bonsai journey with nursery stock and are bound to run into this occasionally. Obviously if you are working with material developed with bonsai in mind from the get go you won’t have this issue.

This is definitely part of what I’m saying and thinking. The nebari was buried from the initial potting before I acquired these, so I tried to work all sides appropriately, but the top of the root ball was notably dense and raised, especially after I titled the potting angle.

Edit to add: I think I may just remove some substrate below the trees, as well as remove some material from the bottom on each tree. Removing substrate may even be enough.

All best,
MG

 

[leatherback]

In this case it seems it might be proper to excavate from the top and reduce the root ball from the top at least down to the nebari.

You find the top of the main roots first. Then you work up from the bottom.

 

[leatherback]

This is definitely part of what I’m saying and thinking. The nebari was buried from the initial potting before I acquired these, so I tried to work all sides appropriately, but the top of the root ball was notably dense and raised, especially after I titled the potting angle.

Edit to add: I think I may just remove some substrate below the trees, as well as remove some material from the bottom on each tree. Removing substrate may even be enough.

All best,
MG

Keep in mind that cleaning upi the roots and sorting them out is part of creating good bonsai. So doing this right at the start of the process means that your tree is set. Once you have developed as a bonsai, there is a chance that your tree is not as strong as it is right now.

 

[yashu]

 

[MrG]

Keep in mind that cleaning upi the roots and sorting them out is part of creating good bonsai. So doing this right at the start of the process means that your tree is set. Once you have developed as a bonsai, there is a chance that your tree is not as strong as it is right now.

yep definitely understood! I did a lot of root work for this very reason, just perhaps not enough removal from the bottom. Or perhaps just too much substrate.

What does your last sentence mean?

 

[MrG]

Hey Folks,

For the sake of discussion, I just saw this photo that illustrates the sort of style of this more mounded look that I mentioned liking.



I am curious, do you all feel that this has too much mounding above the pot line? I clearly wouldn’t be so bold as to suggest my trees are anywhere near this quality but wanted to bring this up for discussion.

All best,
MG

 

[Eckhoffw]

No. The mounding is very nice. There’s nothing wrong with the mound in itself, it’s an attractiveI look. I think It’s the work it takes to properly water the tree.

As you see, the moss is holding it all together. Without it, it’s washing away every watering.


Either way, You still want to have a nice radial system of surface roots (if you can get it) on top of the mound. Therefore, defining those primary roots that will make up your Nabari is crucial either way. You can then continue mounding your tree if desired.

 

[bwaynef]

You'll notice the tree size to pot size ratio on your example is pretty high. It's also literati which brings its own unique guidelines. If you browse Kimura's book and most Kokufu albums, you'll see that mounding is mostly used in particular cases. Shohin, and literati allow for mounding. Recent angle changes sometimes require mounding, but almost always are dealt with in future repots to bring the soil level down to just below the rim of the pot and flat. Kimura's work is particularly flat.

I think if these trees found their way to my yard, I wouldn't hesitate to reduce the rootballs further, find the nebari, and plant them with the soil surface flat, just below the rim of the pot.

 

[MrG]

No. The mounding is very nice. There’s nothing wrong with the mound in itself, it’s an attractiveI look. I think It’s the work it takes to properly water the tree.

As you see, the moss is holding it all together. Without it, it’s washing away every watering.


Either way, You still want to have a nice radial system of surface roots (if you can get it) on top of the mound. Therefore, defining those primary roots that will make up your Nabari is crucial either way. You can then continue mounding your tree if desired.

Ok very good - thank you! Definitely hear you on this, and I think one mistake I made is just adding too much topsoil on these trees which exacerbates the height. I’m going to fix that.

You'll notice the tree size to pot size ratio on your example is pretty high. It's also literati which brings its own unique guidelines. If you browse Kimura's book and most Kokufu albums, you'll see that mounding is mostly used in particular cases. Shohin, and literati allow for mounding. Recent angle changes sometimes require mounding, but almost always are dealt with in future repots to bring the soil level down to just below the rim of the pot and flat. Kimura's work is particularly flat.

I think if these trees found their way to my yard, I wouldn't hesitate to reduce the rootballs further, find the nebari, and plant them with the soil surface flat, just below the rim of the pot.

This is very interesting and I will look into Kimura’s book - I have not seen. These trees are Shohin, so maybe all hope is not lost

I’ll probably try to adjust these repots to lower them slightly although I’m reluctant to damage them.

 

[Shibui]

Removing excess soil from the surface can be done any time. The feeder roots that provide feed and water for the tree are down in the pot and won't be affected by scraping away some surface soil.
You may uncover a few feeder roots as you work down but there should be more than enough down deeper - unless your recent repot was really severe.
Uncovering the thicker roots does not affect them or the tree. Thick roots are akin to a branch above ground. It's only a conduit from root tips to leaves. Thicker roots are also covered with bark. When exposed to air the bark will harden and be exactly like bark on the trunk.

If you feel you've gone far enough you can stop at any time and leave the tree to adjust then come back and go further when the tree and roots have adjusted to the new soil level. Exposed feeder roots will die off as they dry out but the tree will compensate by growing more deeper in the soil.

The scenario mentioned by @yashu where deer roots have grown upward to colonise the upper soil is a case where you may need to work in stages or do a full repot to try to work out which roots to bend down and which to cut entirely.
Need to treat each species according to how well they respond to root pruning.

IMHO that pine shown above is a bit high in the pot. I prefer to see trees actually planted IN the pot rather than above the pot.