Inorganic soil repotting - what's the point?

[JackHammer]

I am having trouble figuring this out.

Many will use inorganic soil for their bonsai and only use ferts/soil supplements for nutrients.

If this is true, why change the soil at all? Akadama will break down so maybe that is the only thing that should be replaced?

Another exception would be a rootbound tree that would require a repot with a root trim or potentially a larger pot.

Even for organic soil- eventually, it becomes depleted of nutrients and would act similar to inorganic soil in that regard. Aside from rootbound plants, what's the point?
I know on a fundamental level, my trees have done better after repots but aside from more available organic nutrients, I don't know why. In the case of inorganic soil, I don't know how a repot would be largely beneficial.

 

[Wires_Guy_wires]

Air.

In a small pot like a bonsai pot, you want lots of air. If organic soil would act and behave like inorganic, I'd never change the soil.
But it doesnt. It's fundamentally different. Best way to understand that is to just try it.

Or look at that less recent thread where someone wanted to understand soil dynamics.

Introductory soil physics

Hi Scott, I read most of the messages and comments in the previous 14 pages of this article and I have this question that I would like to ask you. So, once the top soil dries up (and I'm talking something about turface or calcined or any particle that can absorb and hold water inside itself in...

www.bonsainut.com

 

[Forsoothe!]

Air. How does it get into the Earth, but not into a pot with the same soil? Nursery trees regularly come in giant clay balls in burlap, and yet they look at least good enough to buy. Years and years and years in clay and then it's an emergency repot to get the tree out of that terrible clay it's lived in for 15 years. I detect a mixed metaphor. Giggle, giggle...

 

[Dav4]

Air. How does it get into the Earth, but not into a pot with the same soil? Nursery trees regularly come in giant clay balls in burlap, and yet they look at least good enough to buy. Years and years and years in clay and then it's an emergency repot to get the tree out of that terrible clay it's lived in for 15 years. I detect a mixed metaphor. Giggle, giggle...

Perched water in a shallow pot significantly affects water and air ratios in a large portion of the usable volume of said pot… combined with heavily organic soil, which collapses quickly when kept moist, can result in a sodden mess. Organic soils work much better in taller pots where perched water isn’t an issue.

 

[River's Edge]

I am having trouble figuring this out.

Many will use inorganic soil for their bonsai and only use ferts/soil supplements for nutrients.

If this is true, why change the soil at all? Akadama will break down so maybe that is the only thing that should be replaced?

Another exception would be a rootbound tree that would require a repot with a root trim or potentially a larger pot.

Even for organic soil- eventually, it becomes depleted of nutrients and would act similar to inorganic soil in that regard. Aside from rootbound plants, what's the point?
I know on a fundamental level, my trees have done better after repots but aside from more available organic nutrients, I don't know why. In the case of inorganic soil, I don't know how a repot would be largely beneficial.

Combining substrate to create optimal growing environment. Then adapting to suit ones climate , resources and care routine. inorganic has the advantage of retaining shape, size for longer periods of time without significant decomposition.
Why change the soil at all? the space available for growth gets taken up by growth over time.
Suggest you take advantage of the resource section as suggested. The explanations are clear and complete.

 

[Wires_Guy_wires]

Air. How does it get into the Earth, but not into a pot with the same soil? Nursery trees regularly come in giant clay balls in burlap, and yet they look at least good enough to buy. Years and years and years in clay and then it's an emergency repot to get the tree out of that terrible clay it's lived in for 15 years. I detect a mixed metaphor. Giggle, giggle...

Oh yeah! I love some good organics, even clay!
In nursery pots that is. Roomy, large pots, where gravity and capillary action can do their magic.
I think it can be done! All organic. It's just a lot of effort and time. I like spending my time on the internet instead.

 

[Ohmy222]

I am having trouble figuring this out.

Many will use inorganic soil for their bonsai and only use ferts/soil supplements for nutrients.

If this is true, why change the soil at all? Akadama will break down so maybe that is the only thing that should be replaced?

Another exception would be a rootbound tree that would require a repot with a root trim or potentially a larger pot.

Even for organic soil- eventually, it becomes depleted of nutrients and would act similar to inorganic soil in that regard. Aside from rootbound plants, what's the point?
I know on a fundamental level, my trees have done better after repots but aside from more available organic nutrients, I don't know why. In the case of inorganic soil, I don't know how a repot would be largely beneficial.

You are technically correct but most repots are (or should be) done because the roots need to be cut back to increase air flow not on a random calendar. I do repot annually on small pre-bonsai stuff since I am trying to establish a good base nebari and build from the ground up. Outside of that though I don't repot just to repot.

Since you are doing that it is pretty difficult to save most of the soil. In your Akadama example, it will break down and could use replacement. Lava and pumice will likely not need replacement but to keep the ratio right would would need remixing anyway. I do reuse soil though but not normally on the same tree. Also, I don't remove old soil intentionally. Unless it is really bad I will leave the soil that 'sticks' to tree and add new soil around it. Most of the soil under the trunk I don't mess with.

 

[RKatzin]

Sometimes you have to let go of what you think you know and allow yourself to try something different. This from a man who was staunchly convinced he could grow trees in premium blend organic potting soil. Cut to the chase- I was wrong about that! I didn't just drop everything one day and switch over to inorganic. After killing off the first couple of rounds of tree I started experiments with various mixes and after following the evidence for several years I had to concede that inorganic was the best way to go. I went through a few variations of mixes and gravitated towards more and more pumice and today I have over two hundred trees in containers, almost all in pure pumice. Try it! You'll like it! And your trees will thank you. I haven't lost a tree in a long time.

 

[Paradox]

Air. How does it get into the Earth, but not into a pot with the same soil? Nursery trees regularly come in giant clay balls in burlap, and yet they look at least good enough to buy. Years and years and years in clay and then it's an emergency repot to get the tree out of that terrible clay it's lived in for 15 years. I detect a mixed metaphor. Giggle, giggle...

Nursery trees usually spend only a few weeks in that pot not the years that a bonsai spends in its pot.

Also a tree in the ground where it's roots can grow unhindered is not comparable to one confined in a pot.

Organic soil holds nutrients longer than inorganic soil. A big part of growing and maintaining bonsai is timing of fertilizer. We often withhold fertilizer at certain times to control growth

 

[leatherback]

I am having trouble figuring this out.

Many will use inorganic soil for their bonsai and only use ferts/soil supplements for nutrients.

If this is true, why change the soil at all? Akadama will break down so maybe that is the only thing that should be replaced?

Another exception would be a rootbound tree that would require a repot with a root trim or potentially a larger pot.

Even for organic soil- eventually, it becomes depleted of nutrients and would act similar to inorganic soil in that regard. Aside from rootbound plants, what's the point?
I know on a fundamental level, my trees have done better after repots but aside from more available organic nutrients, I don't know why. In the case of inorganic soil, I don't know how a repot would be largely beneficial.

You repot when the pot has become so full of roots that the tree stops growing and/or water does no longer percolate.For some, this means every 2-4 years. For some that takes a decade.

Of course, in early development you also repot to work on the roots and improve balance between the roots. But once that is done, less is more.

 

[Forsoothe!]

I don't believe you addressed the mechanics of how roots of anything grown in the ground in packed soil survive if the theory of bonsai mix is correct that you need a media so porous you could drive a truck through it. We all know that millions of people use millions of different mixes and most of them survive. Many break all the rules, like for instance the Vietnamese that keep their pots wet in a high humidity, high temperature environment. If the rules can be violated, then they're not "rules".

I don't want to hear that you need the best media (yours) to grow trees well. I, and others do differently and grow as well as you. Your turn.

 

[Shibui]

Nutrient depletion is quite fast in pots. Because we water thoroughly and often the water soluble nutrients are leached out of the pot with draining water every time you water the pot so potted plants become depleted in a matter of weeks. This is why so many successful bonsai growers fertilize often.
Only the very tips of roots can tale in water and nutrients so roots must continually grow to maintain healthy root tips. Depending on the size of the pot the soil must inevitably become full of roots. Only the very tips are actually contributing to plant health but the mass of roots is filling available spaces that should be occupied with air and water. The more the roots fill the pot the harder it becomes to supply enough air and water and plants begin to suffer. This process happens in either organic based or inorganic potting soils. Solutions are to pot into a larger pot to provide more space for further root growth (not ideal for bonsai) or to remove much of the root mass and use the plant's inbuilt mechanisms to regrow new roots in fresh soil that can provide enough air and water. Replacing the spaces in soil appears to be the key to maintaining healthy trees in pots. how often to do that depends on species, age, size of pot and growing conditions. I have not found a one size fits all guideline for how often to repot for optimum plant health in every situation.

Potting soil can be reused but there are several drawbacks: Pest and disease can survive in reused potting soil with devastating results. Is the risk worth the savings? Old potting soil will inevitably break down to some extent depending on the composition and materials used. It will also be full of the previously mentioned roots as well as assorted byproducts of plant growth and fertilization so used soil needs to be cleaned and graded before reuse. Again is the time and effort worth the savings? Obviously everyone will have different views on cost/benefit so some will opt for reuse while other for complete replacement each time.

The relative benefits of organic V inorganic potting soil has been hotly debated many times and debate will no doubt continue. It is possible to grow bonsai in pots in almost any soil but some take a lot of care and effort as mentioned earlier in this thread. My advice has always been to find a soil mix that is readily available and not too expensive but has the required properties for plant health and growth then learn to manage your trees in that soil.

 

[leatherback]

 

[sorce]

Meow you're talking!

Sorce

 

[sorce]

How much potting soil is available on a volcanic Island?

There are probably no less than a thousand things that can be adjusted to use any soil successfully.

Are we not just foolishly trying to mimic?

How many of a thousand things are we willing to adjust.

I use DE and don't do anything special.

Use what makes you not do anything that takes time away from the internet!

Sorce

 

[Adair M]

I don't believe you addressed the mechanics of how roots of anything grown in the ground in packed soil survive if the theory of bonsai mix is correct that you need a media so porous you could drive a truck through it. We all know that millions of people use millions of different mixes and most of them survive. Many break all the rules, like for instance the Vietnamese that keep their pots wet in a high humidity, high temperature environment. If the rules can be violated, then they're not "rules".

I don't want to hear that you need the best media (yours) to grow trees well. I, and others do differently and grow as well as you. Your turn.

It’s not necessary to discuss root growth for trees in the ground. Bonsai live in pots. And what works best for trees in pots is not the same as what works for trees planted in the ground.

Aldo, remember that the bonsai pot is NOT merely aesthetic. A properly sized bonsai pots helps to construct the growth of the tree, to help keep it small and miniaturized. Yes, a bonsai pit restricts root growth. This aids in keeping leaves small and internodes short. Which helps keep the tree in scale.

Modern bonsai soil, a mix of inorganic particle, typically equal parts of akadama, pumice and lava, have proven over time to provide excellent results for bonsai. There may be instances where the mux ratio can be adjusted, but that is beyond the scope of this discussion.

When a bonsai is freshly repotted, some roots are cut back. The tree will want to replace those roots as quickly as it can, the small “feeder” roots are what absorbs water and nutrients. Large roots, by the way, are eliminated as much as possible. Large roots serve to affix trees to the ground. Bonsai don’t need large roots because the trees are firmly secured to their pots with wire. Large roots in a bonsai pot just take up space that can be better used by smaller feeder roots.

So, when the tree is freshly repotted, the new soil is very open, and it is easy for new roots to grow into the empty voids between particles. Thus, the tree rebuilds it’s root system quickly. It’s not unusual to see large leaves and long internodes on the tree just after a repot. Rapid root growth promotes rapid top growth!

But soon, those new roots will hit the sides of the pot, and fill up the easy inter-particle voids. This is where the akadama comes in. Yes, it’s softer than lava and pumice, and it hold water. The feeder roots will latch on, and start to pressure the akadama, causing it to break down. When a particle breaks, it creates new voids for small feeder roots to fill. But, overall, root growth SLOWS down. Now, the top growth slows. Smaller leaves. Shorter internodes. As the akadama breaks down, it holds more water. Which is a good thing, because the top has more leaves to keep hydrated. You see, the akadama changes it’s structure. In a way that helps the tree survive in an artificially small environment!

After some time, the akadama has broken down too much and/or the tree has produced so many roots it’s become root bound. Then, it’s time to repot, and begin the cycle all over. How often does the tree need repotting? It depends! This is where the bonsai artist observes the health of the tree and makes a determination.

But, remember! Growing trees in little pots IS VERY DIFFERENT FROM growing trees in the ground!

Thus is one of the reasons that Master Gardeners often have poor bonsai. They try to treat their trees as if they were growing in the ground. They’re not.

 

[JackHammer]

Nutrient depletion is quite fast in pots. Because we water thoroughly and often the water soluble nutrients are leached out of the pot with draining water every time you water the pot so potted plants become depleted in a matter of weeks. This is why so many successful bonsai growers fertilize often.
Only the very tips of roots can tale in water and nutrients so roots must continually grow to maintain healthy root tips. Depending on the size of the pot the soil must inevitably become full of roots. Only the very tips are actually contributing to plant health but the mass of roots is filling available spaces that should be occupied with air and water. The more the roots fill the pot the harder it becomes to supply enough air and water and plants begin to suffer. This process happens in either organic based or inorganic potting soils. Solutions are to pot into a larger pot to provide more space for further root growth (not ideal for bonsai) or to remove much of the root mass and use the plant's inbuilt mechanisms to regrow new roots in fresh soil that can provide enough air and water. Replacing the spaces in soil appears to be the key to maintaining healthy trees in pots. how often to do that depends on species, age, size of pot and growing conditions. I have not found a one size fits all guideline for how often to repot for optimum plant health in every situation.

Potting soil can be reused but there are several drawbacks: Pest and disease can survive in reused potting soil with devastating results. Is the risk worth the savings? Old potting soil will inevitably break down to some extent depending on the composition and materials used. It will also be full of the previously mentioned roots as well as assorted byproducts of plant growth and fertilization so used soil needs to be cleaned and graded before reuse. Again is the time and effort worth the savings? Obviously everyone will have different views on cost/benefit so some will opt for reuse while other for complete replacement each time.

The relative benefits of organic V inorganic potting soil has been hotly debated many times and debate will no doubt continue. It is possible to grow bonsai in pots in almost any soil but some take a lot of care and effort as mentioned earlier in this thread. My advice has always been to find a soil mix that is readily available and not too expensive but has the required properties for plant health and growth then learn to manage your trees in that soil.

Nutrient depletion- you are saying that nutrients are depleted in a matter of weeks or months. If that is the case, the only difference between organic and inorganic is moisture. After the initial weeks or months have passed of course. Is this correct? This is the confusion I was having. In my mind the argument is moot. Repot for rootbound roots, otherwise, it is ok.

I am not sure I buy the air argument. I have pines that I dug up that are doing quite well in their ball of clay. It might be true, I just want to look for more support.

 

[JackHammer]

Sometimes you have to let go of what you think you know and allow yourself to try something different. This from a man who was staunchly convinced he could grow trees in premium blend organic potting soil. Cut to the chase- I was wrong about that! I didn't just drop everything one day and switch over to inorganic. After killing off the first couple of rounds of tree I started experiments with various mixes and after following the evidence for several years I had to concede that inorganic was the best way to go. I went through a few variations of mixes and gravitated towards more and more pumice and today I have over two hundred trees in containers, almost all in pure pumice. Try it! You'll like it! And your trees will thank you. I haven't lost a tree in a long time.

Sorry, this is anecdotal experience that boils down to "trust me". You may be correct, but I need to do more research.

 

[JackHammer]

It’s not necessary to discuss root growth for trees in the ground. Bonsai live in pots. And what works best for trees in pots is not the same as what works for trees planted in the ground.

Aldo, remember that the bonsai pot is NOT merely aesthetic. A properly sized bonsai pots helps to construct the growth of the tree, to help keep it small and miniaturized. Yes, a bonsai pit restricts root growth. This aids in keeping leaves small and internodes short. Which helps keep the tree in scale.

Modern bonsai soil, a mix of inorganic particle, typically equal parts of akadama, pumice and lava, have proven over time to provide excellent results for bonsai. There may be instances where the mux ratio can be adjusted, but that is beyond the scope of this discussion.

When a bonsai is freshly repotted, some roots are cut back. The tree will want to replace those roots as quickly as it can, the small “feeder” roots are what absorbs water and nutrients. Large roots, by the way, are eliminated as much as possible. Large roots serve to affix trees to the ground. Bonsai don’t need large roots because the trees are firmly secured to their pots with wire. Large roots in a bonsai pot just take up space that can be better used by smaller feeder roots.

So, when the tree is freshly repotted, the new soil is very open, and it is easy for new roots to grow into the empty voids between particles. Thus, the tree rebuilds it’s root system quickly. It’s not unusual to see large leaves and long internodes on the tree just after a repot. Rapid root growth promotes rapid top growth!

But soon, those new roots will hit the sides of the pot, and fill up the easy inter-particle voids. This is where the akadama comes in. Yes, it’s softer than lava and pumice, and it hold water. The feeder roots will latch on, and start to pressure the akadama, causing it to break down. When a particle breaks, it creates new voids for small feeder roots to fill. But, overall, root growth SLOWS down. Now, the top growth slows. Smaller leaves. Shorter internodes. As the akadama breaks down, it holds more water. Which is a good thing, because the top has more leaves to keep hydrated. You see, the akadama changes it’s structure. In a way that helps the tree survive in an artificially small environment!

After some time, the akadama has broken down too much and/or the tree has produced so many roots it’s become root bound. Then, it’s time to repot, and begin the cycle all over. How often does the tree need repotting? It depends! This is where the bonsai artist observes the health of the tree and makes a determination.

But, remember! Growing trees in little pots IS VERY DIFFERENT FROM growing trees in the ground!

Thus is one of the reasons that Master Gardeners often have poor bonsai. They try to treat their trees as if they were growing in the ground. They’re not.

This is really interesting. Am I correct in understanding these 2 points - the focus of a repot is to trim roots, and replace akadama that has broken down? Aside from the root trimming, I am curious how the akadama would differ from an organic substrate that would hold water at a medium density. Fundamentally, it seems like it would do the same thing but maybe the compost would be harder to control. Maybe the moisture density is the major issue for people. I will admit, my vegetables are sometimes hard to control.

My experience with fast growth after a repot is very similar to yours. I also like the concept of using a pot to shape growth, rather than just restrict growth.

 

[Forsoothe!]

By the time roots growing in a high-organic top soil become rootbound they have used-up, or consumed the mineral and organic content that comprised the soil. That much growth of roots can not take place if the media is the typical bonsai mix high in "rocks". The elements or compounds that form the mineral content of typical top soils, which are essentially "fines", are only useful one molecule at a time, oxidized and used by the microorganisms that consume them and excrete compounds that are absorbed by roots and used by plants in the photosynthesis process to make food for plant growth. Only the exterior of the mineral particle is available to be oxidized and used, one molecule at a time. The interior of any mineral particle is not available. The reason why gardens are made up of top soil sized mineral particles is because of the surface area, -the useful surfaces available for oxidization is several orders of magnitude greater than a garden full of bonsai-mix-size-rocks. Also, bonsai mixes tend to use a singular mineral rock or at least rocks of only a few minerals verses typical top soils.

Traditional Japanese bonsai mixes are intended to stop or limit growth. High-organic top soil based mixes are intended to grow at a higher rate, or even a maximized rate. One chooses either end of the scale, or somewhere in-between to meet their own goals, having nothing to do with the passage of air through the mix. Very high growth can be had using a rock-only media just by providing liquids at rates similar to hydroponics. That requires much closer attention to replacing the moisture used/lost in a rock media that doesn't hold as much moisture as typical high-organic mixes. Also, the minerals that are oxidized in typical top soils, being more varied, are less likely to be deficient enough elements to inhibit growth. NPK requirements would not be much different between the two types of media except there is less leaching due to excess water passing through high-organic media because it holds more of the water applied.

Choose your growth rate, choose your poison.