Inorganic soil repotting - what's the point?

[JackHammer]

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.

That's what I was looking for! Thanks!!!!

 

[Adair M]

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.

The problem with organic material in a bonsai pot is organic material can start to rot, and promote root rot. Akadama does break down over time, but since it is a mineral, it doesn’t rot.

Nutrition isn’t provided by the substrate. It’s there to provide a structure for the root system. Nutrition is provided by using organic fertilizer, and micro nutrients as needed. These can be controlled by the bonsai artist.

 

[Adair M]

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.

Bonsai pots are used once the tree has developed, and has entered the refinement stage, where limited growth is preferred. Prior to that, other means of containment are better suited to GROWING bonsai. Mr. Ebihara grew his “million dollar zelkova” in a wooden box for years (decades?) before transferring it to a bonsai pot.

 

[Shibui]

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.

Nutrient depletion is very quick, especially with regular watering. Organic mix may release some more nutrient into the root zone as it decays but nowhere near enough for healthy growth. Additional nutrients must be supplied for potted plants. Some potting soil has nutrient source added. Down here standards mandate that commercial potting soil must have minimum amount of slow release fertilizer included to maintain plants for at least 3 months. After that it is up to the grower.

Repotting is to manage root replacement AND to maintain structure in the soil. You may not want to believe that air is important to roots but that does not make it so. It is possible to grow trees in clay with minimum air but it takes more skill and effort and chances of something going wrong are much higher. You could try side by side trials to see any differences first hand.
Note that clay has a high CEC (cation exchange capacity) so nutrients are held for longer and may be the reason you have not yet noticed starvation in potted plants. Open aerated mix will need more water and more fertilizer but will almost certainly give better growth and health.

 

[JackHammer]

Nutrient depletion is very quick, especially with regular watering. Organic mix may release some more nutrient into the root zone as it decays but nowhere near enough for healthy growth. Additional nutrients must be supplied for potted plants. Some potting soil has nutrient source added. Down here standards mandate that commercial potting soil must have minimum amount of slow release fertilizer included to maintain plants for at least 3 months. After that it is up to the grower.

Repotting is to manage root replacement AND to maintain structure in the soil. You may not want to believe that air is important to roots but that does not make it so. It is possible to grow trees in clay with minimum air but it takes more skill and effort and chances of something going wrong are much higher. You could try side by side trials to see any differences first hand.
Note that clay has a high CEC (cation exchange capacity) so nutrients are held for longer and may be the reason you have not yet noticed starvation in potted plants. Open aerated mix will need more water and more fertilizer but will almost certainly give better growth and health.

I would agree with you, clay is not the best growing medium by far. I have used too much of it in the past, and yes, the plants have had a failure to thrive. The question is pertaining to the cause though. Is that due to air exclusively? It could be, but something tells me there is something else going on with clay in particular. Some plants can thrive in clay soil so maybe it depends on the plant.

 

[Shibui]

More likely it depends on whether the plants are in a pot or in the ground. Soil has very different properties when confined to a container than when it is joined to the entire earth.

 

[Forsoothe!]

More likely it depends on whether the plants are in a pot or in the ground. Soil has very different properties when confined to a container than when it is joined to the entire earth.

I've heard that retort a thousand times over the last twenty years. It didn't mean anything then or now. It's a generality, or better said a conversation stopper that conveys no knowledge or specifics that can be argued one way or the other. It falls into the category of, "Take my word for it; I don't want to be pinned down to specifics".

I would say that soil can be different in a pot, and our cultural methods can also be altered to accommodate whatever those conditions are. There is no soil configuration that cannot be made to work in a pot. Some are easier to be adjusted to than others, but the most important single factor to using this or that media begin and end with the user's care predilections. My watering habits match my plant's needs in my media mix.

Clay works fine for landscape growers because they like Balled & Burlap which holds feeder roots together well for distribution. Plants grow well enough in it for them to make a profit. They never monkey with the roots. B&B works bad for bonsai because you have to destroy all the tiny feeders roots getting the clay off the roots for repotting. So clay is different in the ground verses in a pot but nobody uses clay as a growing media in pots anyway. Soil dams on slabs don't count.

Sand isn't used much in bonsai, if ever, partly because it is hard to confine to a pot unless it is kept wet. Lots of stuff in the real world grows in wet sand, and not much can stand dry sand. Sand in equal parts with organics can be very productive in the real world and works well in a pot without much accommodation.

Not much in the real world grows in rocks without fines, but is the preferred media in bonsai supposedly to provide air to the roots. That is a fiction. Bonsai are grown in rocks to keep them a finished size. It also makes it easier to repot and choose which roots you want to keep and which you want to excise. Since it is barren of nutrients, that also contributes to control over growth allowing the grower to meter exactly the nutrients to his goals. All very important, but all having nothing to do with air.

 

[JackHammer]

I've heard that retort a thousand times over the last twenty years. It didn't mean anything then or now. It's a generality, or better said a conversation stopper that conveys no knowledge or specifics that can be argued one way or the other. It falls into the category of, "Take my word for it; I don't want to be pinned down to specifics".

I would say that soil can be different in a pot, and our cultural methods can also be altered to accommodate whatever those conditions are. There is no soil configuration that cannot be made to work in a pot. Some are easier to be adjusted to than others, but the most important single factor to using this or that media begin and end with the user's care predilections. My watering habits match my plant's needs in my media mix.

Clay works fine for landscape growers because they like Balled & Burlap which holds feeder roots together well for distribution. Plants grow well enough in it for them to make a profit. They never monkey with the roots. B&B works bad for bonsai because you have to destroy all the tiny feeders roots getting the clay off the roots for repotting. So clay is different in the ground verses in a pot but nobody uses clay as a growing media in pots anyway. Soil dams on slabs don't count.

Sand isn't used much in bonsai, if ever, partly because it is hard to confine to a pot unless it is kept wet. Lots of stuff in the real world grows in wet sand, and not much can stand dry sand. Sand in equal parts with organics can be very productive in the real world and works well in a pot without much accommodation.

Not much in the real world grows in rocks without fines, but is the preferred media in bonsai supposedly to provide air to the roots. That is a fiction. Bonsai are grown in rocks to keep them a finished size. It also makes it easier to repot and choose which roots you want to keep and which you want to excise. Since it is barren of nutrients, that also contributes to control over growth allowing the grower to meter exactly the nutrients to his goals. All very important, but all having nothing to do with air.

I don't want to defend a bad argument but I do believe there is a different eco system in the ground vs a pot. There is a dense fungal and microbial network joining plants and transferring nutrients in an old growth forest and this is largely missing from a pot.
This leads me to the conclusion that these two environments should be treated differently and I think most logical parties would agree.

 

[Forsoothe!]

@JackHammer says "...There is a dense fungal and microbial network joining plants and transferring nutrients in an old growth forest and this is largely missing from a pot."

The microbial population is only different if you use a media that is different. If one chooses to change to different media that doesn't support or contain the original microbial population, that is an active choice. It doesn't have to be.

 

[Potawatomi13]

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.

2014 First trip to visit Ryan Neil. Besides just seeing his trees being eye opening instructional by itself personal huge question was what is best substrate for pines(specifically Ponderosas). His answer pumice. Sure I asked why but can't remember. Good sense told me he KNOWS what he says however wrapping personal courage around idea of potting in rocks took some mental wrestling. 2016 Spring came time to pot trees bought from Randy Knight in 2015 and since have not looked back. Pumice filled with air spaces, holes, passages that hold H20, fertilizer, spaces between rocks hold air. Great/perfect for most trees needs and pretty well prevents eventuality of ever overwatering with excellent drainage. Only time using any lava is in tall pot for added weight in bottom only. Lava less H2O retentive so not so useful.

 

[Potawatomi13]

Not much in the real world grows in rocks without fines, but is the preferred media in bonsai supposedly to provide air to the roots. That is a fiction. Bonsai are grown in rocks to keep them a finished size. It also makes it easier to repot and choose which roots you want to keep and which you want to excise. Since it is barren of nutrients, that also contributes to control over growth allowing the grower to meter exactly the nutrients to his goals. All very important, but all having nothing to do with air.

A statement of outright ignorance. Ask Ryan Neil to see how far this statement goes?

 

[JackHammer]

@JackHammer says "...There is a dense fungal and microbial network joining plants and transferring nutrients in an old growth forest and this is largely missing from a pot."

The microbial population is only different if you use a media that is different. If one chooses to change to different media that doesn't support or contain the original microbial population, that is an active choice. It doesn't have to be.

I agree, though, I am not sure how it would change over time. I guess every re-potting would be a chance to make that choice again.
The nuance here is that forest trees are growing with companions. Outside of a forest planting, we typically don't see this.

 

[JackHammer]

2014 First trip to visit Ryan Neil. Besides just seeing his trees being eye opening instructional by itself personal huge question was what is best substrate for pines(specifically Ponderosas). His answer pumice. Sure I asked why but can't remember. Good sense told me he KNOWS what he says however wrapping personal courage around idea of potting in rocks took some mental wrestling. 2016 Spring came time to pot trees bought from Randy Knight in 2015 and since have not looked back. Pumice filled with air spaces, holes, passages that hold H20, fertilizer, spaces between rocks hold air. Great/perfect for most trees needs and pretty well prevents eventuality of ever overwatering with excellent drainage. Only time using any lava is in tall pot for added weight in bottom only. Lava less H2O retentive so not so useful.

If you need to create a dry environment, using pumice makes sense to me.

 

[Bonsai Nut]

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.

^This^

Why repot a container grown plant?
(1) To do root maintenance.
(2) To open up the soil mass.
(3) To replace broken down media.

If you don't repot a containerized tree, it may in time choke itself to death. The root mass continues to grow until it occupies every bit of void space. Oxygen is depleted, and water has a hard time penetrating the interior. Eventually the rootball consists of dead zones of choked dead roots with scattered pockets of live roots throughout. Tree growth slows to a crawl, and may stop altogether. You may get dead branches or tree die-back due to root death. When you go to repot a tree that has been in this condition for years, you usually find that much of the potting media has broken down into smaller particles - particularly "softer" media like acadama and pumice, but even harder rock like lava. You might be able to reuse some of it if you rinse it, let it dry in the sun for a couple of weeks, and then screen it, but most people find it easier just to replace it.

If you need to create a dry environment, using pumice makes sense to me.

And just going to say - if you consider pumice a "dry" environment, you are using the wrong pumice. Good pumice will hold water like a sponge - without causing saturated swamp-like conditions.

 

[Paradox]

^This^

Why repot a container grown plant?
(1) To do root maintenance.
(2) To open up the soil mass.
(3) To replace broken down media.

The first two points are related. If you don't repot a containerized tree, it may in time choke itself to death. The root mass continues to grow until it occupies every bit of void space. Oxygen is depleted, and water has a hard time penetrating the interior. Eventually the rootball consists of dead zones of choked dead roots with scattered pockets of live roots throughout. Tree growth slows to a crawl, and may stop altogether. You may get dead branches or tree die-back due to root death. When you go to repot a tree that has been in this condition for years, you usually find that much of the potting media has broken down into smaller particles - particularly "softer" media like acadama and pumice, but even harder rock like lava. You might be able to reuse some of it if you rinse it, let it dry in the sun for a couple of weeks, and then screen it, but most people find it easier just to replace it.


And just going to say - if you consider pumice a "dry" environment, you are using the wrong pumice. Good pumice will hold water like a sponge - without causing saturated swamp-like conditions.

Trees can actually push themselves out of the pot if they are not repotted or even break a pot. They need to be repotted regularly.

Good way to describe pumice, I was trying to figure out how to explain it. I was amazed when I first bought some pumice and felt how damp it got on humid days while it was sitting in a garbage bag. It even pulls water out of the air.

 

[Adair M]

^This^

Why repot a container grown plant?
(1) To do root maintenance.
(2) To open up the soil mass.
(3) To replace broken down media.

If you don't repot a containerized tree, it may in time choke itself to death. The root mass continues to grow until it occupies every bit of void space. Oxygen is depleted, and water has a hard time penetrating the interior. Eventually the rootball consists of dead zones of choked dead roots with scattered pockets of live roots throughout. Tree growth slows to a crawl, and may stop altogether. You may get dead branches or tree die-back due to root death. When you go to repot a tree that has been in this condition for years, you usually find that much of the potting media has broken down into smaller particles - particularly "softer" media like acadama and pumice, but even harder rock like lava. You might be able to reuse some of it if you rinse it, let it dry in the sun for a couple of weeks, and then screen it, but most people find it easier just to replace it.


And just going to say - if you consider pumice a "dry" environment, you are using the wrong pumice. Good pumice will hold water like a sponge - without causing saturated swamp-like conditions.

Trees in a pot get potbound, they create a mat of roots around the sides and across the bottom. These mats can get thick, and dense. And clog up the drain holes, which can lead to them not draining. At this point, the roots would be sitting in water. Which can drown them, and root rot can set in.

 

[Paradox]

Trees in a pot get potbound, they create a mat of roots around the sides and across the bottom. These mats can get thick, and dense. And clog up the drain holes, which can lead to them not draining. At this point, the roots would be sitting in water. Which can drown them, and root rot can set in.

Had this happen to a JBP. If I hadnt noticed the problem in time, the tree would have probably continued to decline and die