Acer Rubrum/Red Maple Prebonsai Repotting - Results of Fabric Grow Pot + Ebihara Method + Crappy Substrate

[jeef16]

This red maple is going to be entering it's fourth grow season of its life. It started out as a 'weed' in this very fabric grow pot that housed a tomato plant. Then I left it in there the second year without repotting to let it get vigorous. the third year, I repotted it in some very mid substrate for some reason, idk why. it was mostly boon soil scrap mixed with coarse perlite and some crappy topsoil, for some reason. I planted this on top of some random plastic drain tray for a succulent pot as a quick and dirty ebihara method and it worked quite well. Some wire bite from last year means this wont be a beauty queen most likely unless it gets really thick and barky. I may end up just cutting right above that first low branch and using that as my new leader to develop the tree, that way the scarring is very limited even though it means a setback of like 2 years.

I'm repotting it from a 5gal pot to a 3gal, and using a 70/30 mix (roughly) of small perlite/coco coir. This gives me a very moist but airy substrate, and combined with the extra moisture retained by the fabric pot, creates a growing environment that is very wet but has access to as much oxygen as needed. I've found that my other red maples (which were also in 5gal fabric pots, no plastic tray, substrate of 70/30 coarse perlite+compost) respond very well to these conditions. the smaller particle size will encourage finer roots, and will be even wetter. These maples are native to my area of new york which is very wet, so I theorize these that my new substrate will push even more growth.

You can see the crappy soil in pics 2 and 3.

pic 4:: escape roots from last year's growth

pic 5, 6: after shaking the tree upside down to get all loose soil out, you can see how the roots are air pruned very radially. air pruning encourages feeder roots to grow and shows that even with my crappy soil, we still get zero root rot and vigorous growth

pic 7 bottom of the pot after tree removal. minimal root circling as most found their way through the fabric

pic 8, 9, 10: after knocking soil out some more, you can see the tray I planted it on. pretty much no root growth in the center, I'd need a few growing seasons to achieve that.

pic 11. 12, 13: cleaning off the roots after cutting off everything that was vertical. pretty convenient to grow this way, makes it quick to get to the actual important work. you can see how well the plastic tray worked to encourage radial rooting, but the ebihara method is always prone to crossing roots.

pic 14: radical root cutback. this was about what I cut back to last growing season when I initially planted it on the tray. even with crappy substrate, the fabric pot + ebihara method produces very quick results. the roots werent anywhere close to as nebari-like last year.

pic 15, 16: potted back up. I didn't show it, but I always put a spagnum top dressing or a layer of extra large perlite on top. the small perlite is easily pushed by your watering, and perlite in general is extremely light so it has trouble stabilizing a tree. combined with a fabric grow pot, you dont have much in the way of support. I've found the spagnum top dressing holds everything very firm until the tree can establish and stabilize itself. coarse perlite can achieve similar things by creating a reverse drainage layer,, allowing the water to gently flow down onto the small perlite instead of everything getting pushed around.

will post next year's growth, quite happy with these fabric grow pots for early prebonsai development. I'm using a mix of 1 and 3 gallon for my prebonsai currently. the major downside to these pots is you cant wire your trees down to them,, the most you can do is use some plant on the rim of the bag but the fabric makes true stabilization quite hard. but I've found that if you plant deeper and be careful, it's really no problem. hopefully this inspires some of you to try a fabric grow pot!

 

[Shibui]

I've read through most of the original post.
What is the point? You've brutalised all the accepted techniques for growing stock and appeared to have ended up with a trunk very similar to the starting point.
What do you think you have achieved or is this just a starting point?

 

[Gabler]

I'm not sure it's clear to me what the starting point was. I don't think these are before and after photos. That is to say, it looks like OP just took a tree out of bad soil, worked the roots, and repotted it into better-drained soil, probably all within one hour. We'll have to check back later to see any progression.

 

[jeef16]

I've read through most of the original post.
What is the point? You've brutalised all the accepted techniques for growing stock and appeared to have ended up with a trunk very similar to the starting point.
What do you think you have achieved or is this just a starting point?

>What is the point?

the point of using a fabric grow pot? of growing on a tray? of using perlite? idk which specifically you're talking about, but the fabric pots have larger volumes than the typical anderson flat. Larger volume = more roots = larger uptake of nutrients = more growth, And not just any roots, but you can see how many feeder roots have been established with literally no root rot, or root circling. prebonsai is sometimes developed in containers such as colanders, not only because they're well draining and allow a ton of air to get to the roots, but also because the roots get air-pruned and develop fine feeder roots much easier. As you can see in the post, it was quite successful at that! You should try using colanders for conifers, it helps develop fine feeder roots and keeps the soil conditions better suited for conifers especially pines if you're unfamiliar with that technique. This fabric pot is like a colander, except bigger and softer haha.

> You've brutalised all the accepted techniques for growing stock

care to elaborate? I personally dont see how I've done so, that seems a bit dramatic of a response lol. I'm using well draining, airy soil (kind of, thats why I'm repotting to better soil) and the ebihara-style of nebari development. Seems pretty orthodox to me. The only non traditional aspect is that I'm using 3 and 5 gallon containers instead of 1 gallon containers, if I had to guess. If I was ground-growing this tree, would you also be saying I'm brutalizing the accepted techniques ? I'm just gonna keep doing what I'm doing though, it seems to be working very well (especially if it provokes dramatic responses from forum posters. when I grow bonsai, I shock everyone who sees, even myself!)

>appeared to have ended up with a trunk very similar to the starting point.

I'm a bit confused here. Do you think that pic 1 and pic 16 were taken a year apart? of course the trunk looks similar to the starting point, a tree can't grow that fast while it's being repotted silly! the photos were taken an hour apart so it's no surprise the trunk didn't change. you should have no reference as to what this tree looked like last year, so you can't really claim that it appears nothing has happened to this tree...unless you broke into my back yard haha

>What do you think you have achieved

What this post is about is a seedling about to enter it's 4th growing season. I'm repotting this tree to prepare it for the 2025 growing season. I did not post or take any pics of its size before the 2024 growing season, so there is not before/after pics. I can show you a red maple seedling I have that would roughly show what the tree looked like before its 2024 growth if you'd like to see an actual before/after of how the fabric pot affected growth.

In terms of achievement, I'd say I'm quite pleased! For trunk growth, I'd say it about doubled its thickness during the 2024 growing season. In spring 2024 it was around 5-6mm thick and in spring 2025, its about 10mm thick. if I didn't trim the long branches and repot this year, I could probably push it over 1.5-2cm thick.

As for achievements in root growth, I think this is more notable than the trunk growth. As I said before (I know you didnt fully read the post haha), I cut the roots back in 2024 as far back as I did just the other day in pic 15. The roots were not even close to as thick or nebari-like as they were last year, and there is plenty of evidence on the ebihara method working wonders. But just look at how much root growth occurred. It went from a small area covering a tiny tray (to reiterate, pic 15 WAS NOT taken last year, it was taken a few days ago. But in terms of how much I cut back, it's basically the same). So I went from basically no roots to everything you see in pic 8 from a single growing season. if that isnt vigorous growth, then idk what is.

If I had to make a conclusion for my achievements for this tree, I would say: even if you have kind of crappy soil, using a large fabric air pot + ebihara style of nebari development can still produce shocking results. I believe the fabric grow pot can take most of the credit for the vigorous growth.

 

[jeef16]

I'm not sure it's clear to me what the starting point was. I don't think these are before and after photos. That is to say, it looks like OP just took a tree out of bad soil, worked the roots, and repotted it into better-drained soil, probably all within one hour. We'll have to check back later to see any progression.

this was just about a repot I did the other day, no progress pic here haha. I can take a pic of a maple that's 1 year younger than the one in this post if you want to see a real before/after. this post was to demonstrate that even with crappy soil, you can get great results using these fabric grow pots which are essentially just bigger colanders. You can capture some of the vigor of ground-growing by using very big containers, but the risk of using a 5gal nursery pot is that too much moisture will be retained and not enough air can get to the roots to truly take advantage of the increased root mass. it's like if you're lifting weights constantly but not hitting your protein requirements - you'll always be short a critical element that will push the muscle growth to the limit. The fabric air pot lets the tree get all the oxygen it needs, develop fine feeder roots via air-pruning, and retain slightly more moisture than colanders (or rather, dries out at a slower rate) which deciduous trees respond extremely well to in my experience. Maples loooove wet soil.

 

[Gabler]

this was just about a repot I did the other day, no progress pic here haha. I can take a pic of a maple that's 1 year younger than the one in this post if you want to see a real before/after. this post was to demonstrate that even with crappy soil, you can get great results using these fabric grow pots which are essentially just bigger colanders. You can capture some of the vigor of ground-growing by using very big containers, but the risk of using a 5gal nursery pot is that too much moisture will be retained and not enough air can get to the roots to truly take advantage of the increased root mass. it's like if you're lifting weights constantly but not hitting your protein requirements - you'll always be short a critical element that will push the muscle growth to the limit. The fabric air pot lets the tree get all the oxygen it needs, develop fine feeder roots via air-pruning, and retain slightly more moisture than colanders (or rather, dries out at a slower rate) which deciduous trees respond extremely well to in my experience. Maples loooove wet soil.

I was responding to Shibui as much as I was responding to you. I was trying to figure out why he had such an uncharacteristically negative response to your post. I know it was intended to elicit a thoughtful discussion, because that's always how he is, but beyond that, I'm not sure what he was getting at.

 

[jeef16]

I was responding to Shibui as much as I was responding to you. I was trying to figure out why he had such an uncharacteristically negative response to your post. I know it was intended to elicit a thoughtful discussion, because that's always how he is, but beyond that, I'm not sure what he was getting at.

eh whatever lol. I'll post updates with this summer's growth. The wire scarring looks worse in the pics than it does in person, but I may just chop at the lowest tiny branch and redevelop from there. I'll lose a year or so, but the combo of a kinda contrived wiring shape + wire bite + young enough material means I should probably just do the chop before I get full bud break. I know it's a double stress, but these red maples are tough and vigorous. and reducing the foliage mass will lighten the load on the roots as well. Normally I'd just leave everything to thicken up for a few years before chopping back to a stump and redeveloping from there, but I already have quite a few red maples I'm planning to do that on anyways so developing this one a little slower may be nice. Maybe I'll turn it into a small shohin?

 

[Gabler]

Thicken your trunk and then cut back to the tiny branch (which by then will be a big branch).

 

[Shibui]

the point of using a fabric grow pot? of growing on a tray? of using perlite? idk which specifically you're talking about, but the fabric pots have larger volumes than the typical anderson flat. Larger volume = more roots = larger uptake of nutrients = more growth, And not just any roots, but you can see how many feeder roots have been established with literally no root rot, or root circling. prebonsai is sometimes developed in containers such as colanders, not only because they're well draining and allow a ton of air to get to the roots, but also because the roots get air-pruned and develop fine feeder roots much easier. As you can see in the post, it was quite successful at that! You should try using colanders for conifers, it helps develop fine feeder roots and keeps the soil conditions better suited for conifers especially pines if you're unfamiliar with that technique. This fabric pot is like a colander, except bigger and softer haha.

Thanks for posting your work and thanks for the clarifications on what the original post was about. It appears some of my initial interpretations were not accurate.
I'm not trying to stop you doing what you believe is good practice, in fact, I love it when growers try out new and innovative twists on existing techniques. That's where progress comes from.
I have been developing trees for bonsai for around 40 years and have tested almost every method and type of grow pot, usually with multiple trees and over longer timeframes so I think I do have some experience with these concepts but have somehow come to slightly different conclusions to yours.

I agree that larger volume = more roots = more growth.
I have not tested grow bags with crappy soil but I suspect you are correct that the better drainage of the fabric grow bag has allowed you to get good results with less than ideal soil.

However, I have not found that colanders or grow bags result in finer feeder roots developing easier. Just because you see feeder roots on this tree that was grown in a fabric bag does not mean the bag is responsible. I have done comparative trials over years and found very little difference between root mass of trees grown in standard pots and trees grown in bags or colanders. The bags do help produce more finer roots right out close to the bag due to air pruning but those roots will all be chopped off (as shown in your photos). Circling roots in standard pots are also no problem because they will be chopped off as we develop the nebari. Any root that's allowed to grow, will thicken the root closer to the trunk if that's what you mean by developing nebari. It does not seem to matter whether the root is air pruned or not, we still end up with thicker roots close to the trunk just because the roots are growing.
Just to be clear, my understanding of air pruning is that roots that reach the bag (or edge of air pruning pot) stop growing as the root tips hit the air. Air pruning does not happen closer to the centre of the container. Air pruned roots do develop new growing points as a response to the air pruning but closer examination of a number of these root systems showed virtually all the new root growth was close to the air pruning site rather than uniformly back along the main roots.

One thing I can predict with some certainty is that next repot you will find your root system will have lots more root ramification. Maybe you will conclude that's also due to the fabric bag or to Ebihara. My experience suggests it will be due to the root prune you've done this time. I see increase in root ramification after root pruning in most of the maples I grow here without the magic of fabric pots or Ebihara boards.

My other beef is with Ebihara boards. Again, I've tried this technique extensively since it was first published. Sometimes I get great roots, sometimes not. Growers don't seem to post their failures when using this technique, only the best successes so it appears to be almost magically effective. When I grow trees without Ebihara boards, sometimes I get great roots and sometimes not. Are the boards responsible or is there something else happening here?

Now you have replanted the tree with established horizontal roots back onto the same tray, Ebihara style, and, when you repot next and find a flat root system, it is likely that you will again credit the board/tray with producing that root system. At least those are the claims I've seen form many others following this path. My experience is that once a horizontal root system is established, that horizontal root system will continue to develop with or without anything under it. The boards at this stage appear to be redundant. I now leave the boards out after the first round and still end up with a similar horizontal root system, even after 5-10 years of ground growing.

In terms of achievement, I'd say I'm quite pleased! For trunk growth, I'd say it about doubled its thickness during the 2024 growing season. In spring 2024 it was around 5-6mm thick and in spring 2025, its about 10mm thick.

Congratulations on the growth rate. That may be a great growth rate for your area but we can't be sure unless we have some control trees to measure against.

if I didn't trim the long branches and repot this year, I could probably push it over 1.5-2cm thick.

What would be your prediction for growth rate be with the repot and trim the long branches? and how do you think the 2 different methods (root prune and trim V left to grow unpruned) would affect the longer term development rates and quality of the final bonsai?
I only ask because I do have extensive experience using both methods and my conclusions seem to differ from most inexperienced growers.

Thanks again for your patience with me being pedantic and hope you don't feel I'm making any personal criticism of you, the post or the techniques you are trying.

 

[pandacular]

Congratulations on the growth rate. That may be a great growth rate for your area but we can't be sure unless we have some control trees to measure against.

I must confess, I came into this thread wondering what exactly was being shown off like you Neil. For a four year old plant, it’s not particularly strong, nor does it have any characteristics that would allow me to draw assumptions, much less conclusions.

To the original poster, note that Shibui is a long seasoned grower who—I’m told by those who know—is one of the finest on his entire continent. He has the experience and foresight to plan high quality production. The attitude expressed in this post could be described as lackadaisical at best, so where he has given you a great deal of information at no cost, you should take as much of it to heart as possible.

 

[jeef16]

Thanks for posting your work and thanks for the clarifications on what the original post was about. It appears some of my initial interpretations were not accurate.
I'm not trying to stop you doing what you believe is good practice, in fact, I love it when growers try out new and innovative twists on existing techniques. That's where progress comes from.
I have been developing trees for bonsai for around 40 years and have tested almost every method and type of grow pot, usually with multiple trees and over longer timeframes so I think I do have some experience with these concepts but have somehow come to slightly different conclusions to yours.

I agree that larger volume = more roots = more growth.
I have not tested grow bags with crappy soil but I suspect you are correct that the better drainage of the fabric grow bag has allowed you to get good results with less than ideal soil.

However, I have not found that colanders or grow bags result in finer feeder roots developing easier. Just because you see feeder roots on this tree that was grown in a fabric bag does not mean the bag is responsible. I have done comparative trials over years and found very little difference between root mass of trees grown in standard pots and trees grown in bags or colanders. The bags do help produce more finer roots right out close to the bag due to air pruning but those roots will all be chopped off (as shown in your photos). Circling roots in standard pots are also no problem because they will be chopped off as we develop the nebari. Any root that's allowed to grow, will thicken the root closer to the trunk if that's what you mean by developing nebari. It does not seem to matter whether the root is air pruned or not, we still end up with thicker roots close to the trunk just because the roots are growing.
Just to be clear, my understanding of air pruning is that roots that reach the bag (or edge of air pruning pot) stop growing as the root tips hit the air. Air pruning does not happen closer to the centre of the container. Air pruned roots do develop new growing points as a response to the air pruning but closer examination of a number of these root systems showed virtually all the new root growth was close to the air pruning site rather than uniformly back along the main roots.

One thing I can predict with some certainty is that next repot you will find your root system will have lots more root ramification. Maybe you will conclude that's also due to the fabric bag or to Ebihara. My experience suggests it will be due to the root prune you've done this time. I see increase in root ramification after root pruning in most of the maples I grow here without the magic of fabric pots or Ebihara boards.

My other beef is with Ebihara boards. Again, I've tried this technique extensively since it was first published. Sometimes I get great roots, sometimes not. Growers don't seem to post their failures when using this technique, only the best successes so it appears to be almost magically effective. When I grow trees without Ebihara boards, sometimes I get great roots and sometimes not. Are the boards responsible or is there something else happening here?

Now you have replanted the tree with established horizontal roots back onto the same tray, Ebihara style, and, when you repot next and find a flat root system, it is likely that you will again credit the board/tray with producing that root system. At least those are the claims I've seen form many others following this path. My experience is that once a horizontal root system is established, that horizontal root system will continue to develop with or without anything under it. The boards at this stage appear to be redundant. I now leave the boards out after the first round and still end up with a similar horizontal root system, even after 5-10 years of ground growing.


Congratulations on the growth rate. That may be a great growth rate for your area but we can't be sure unless we have some control trees to measure against.

What would be your prediction for growth rate be with the repot and trim the long branches? and how do you think the 2 different methods (root prune and trim V left to grow unpruned) would affect the longer term development rates and quality of the final bonsai?
I only ask because I do have extensive experience using both methods and my conclusions seem to differ from most inexperienced growers.

Thanks again for your patience with me being pedantic and hope you don't feel I'm making any personal criticism of you, the post or the techniques you are trying.

>However, I have not found that colanders or grow bags result in finer feeder roots developing easier. Just because you see feeder roots on this tree that was grown in a fabric bag does not mean the bag is responsible. I have done comparative trials over years and found very little difference between root mass of trees grown in standard pots and trees grown in bags or colanders. The bags do help produce more finer roots right out close to the bag due to air pruning but those roots will all be chopped off (as shown in your photos).

that's a fair response. personally I've found that at least on my acer rubrums in downstate NY that are in fabric/colander type vessels do produce finer roots than some I've planted in random 1gal nursery containers I have laying around, which produce thicker and more typical looking roots you'd see in a 'standard' pot. I wouldn't say the root *mass* would be radically different from any container of the same volume, but its just my personal observation that I consistently get these finer roots with these containers. If anything changes or I notice that I no longer get the fine root growth, I'll probably change something (this specific tree is most likely going in an anderson flat next year anyways. Other potential factors that increased fine rooting in this pot was the coarse perlite. I've found that perlite encourages fine roots to penetrate through the particle, kind of like akadama. Going to see what much finer perlite+some coco coir can produce, but I imagine it'll also be a system of fine roots.

For now I'm going to stick to the fabric pots still, regardless of the true science behind root pruning. because the fabric pots still help me achieve something that my maples respond well to: having a container that gives the roots lots of oxygen while having a moister environment than a typical colander/pond basket. while a nursery container would also retain the moisture better than a colander, it would limit the oxygen access to the roots. Balance of water and oxygen, and all that jazz and such. Having a container that is larger than a colander (aside from those absolute giant ones you see in asian restaurants sometimes haha), wetter than a colander, but still lets plenty of air flow to the roots, is I think what's making a bigger impact on my tree's growth than the roots being air pruned. Plus my escape roots probably help too.

>One thing I can predict with some certainty is that next repot you will find your root system will have lots more root ramification. Maybe you will conclude that's also due to the fabric bag or to Ebihara. My experience suggests it will be due to the root prune you've done this time

I do agree with that. it's the main reason I cut back so radically wherever I could. The roots ramify from those thick roots after a cutback, and pushing that as close to the base of the tree as possible. If there's one thing I learned about creating nebari on maples (most of the content I've consumed on this is for JM's but still) is that strong cutbacks close to the trunk will produce the best results. I credit the ebihara board with creating the radial foundation much faster, even though the method itself can be a miss sometimes like you mentioned. But I've had misses with the 'regular' method of standard root pruning + deep planting, and other stuff like using a wire to girdle seedlings. I've gotten mixed results with those methods too and the only thing I can do with the ones "failures" is to keep root pruning, plant deep, and pray haha (I mostly used wire girdling techniques as I have a lot of very young material currently, to try and kickstart the transitioning from a vertical taproot system to a horizontal root system). I think that variation just comes with the territory of trying gimmicks to achieve the best radial rooting possible, and is an excuse to have more bonsai! because hey, at least some of them gotta work out haha. I'd rate the radial rooting of this to be like 8/10 for now. not perfect and definitely heavier on one side, but significantly better than where I was last year. I'd say the 'magic' of it is that the roots thickened much faster while planted on a board vs my acer rubrum's of the same age that were potted normally, which is nice.

>that horizontal root system will continue to develop with or without anything under it. The boards at this stage appear to be redundant. I now leave the boards out after the first round and still end up with a similar horizontal root system

that's good to know, most of my experience with ebihara boards is quite limited especially for very long term progression. I'll remove the plastic tray in the next growing season for sure, especially as it impacts root growth in the center of the pot--which was not an issue for my regular acer rubrum prebonsai. Meaning I did have less root mass in this pot than my other equivalent prebonsai. I mainly planted on the tray this year for surety in technique, after cutting back radically I wanted to try to recreate the vigorous nebari growth again, but starting from a much better foundation. Once i'm happy with how radial the bones of the nebari are, I'll remove the board and pot up in an anderson flat

will definitely post the results of this upcoming season's growth!

 

[jeef16]

The attitude expressed in this post could be described as lackadaisical at best, so where he has given you a great deal of information at no cost, you should take as much of it to heart as possible.

I'll be sure to keep that in mind, and don't worry sir, I'll get this bonsai up to ship-shape! Can I get my quarterly evaluation yet ?