Thickening trunks, organic or inorganic soil?

[PastryBaker]

I have read articles, forums etc on thickening trunks of pre-bonsai and nursery stock, I know planting the tree in the ground helps. I also read that putting them in bigger pots.
I want to know if you put them in bigger pots, does the type of soil matter? Does organic soil work better than inorganic? Or does it matter.

Thanks

 

[Tidal Bonsai]

I have read articles, forums etc on thickening trunks of pre-bonsai and nursery stock, I know planting the tree in the ground helps. I also read that putting them in bigger pots.
I want to know if you put them in bigger pots, does the type of soil matter? Does organic soil work better than inorganic? Or does it matter.

Thanks

I have seen inorganic like pumice work really well, as well as a fine sandy organic mix for thickening trunks. For trees in the ground, I like using inorganic for pond baskets and Anderson flats because the soil doesn’t fall out of them. For big nursery pots out of the ground, I like a sandy organic mix. Having a fine particle size is way more important than the mix for getting a fine root system when you are just growing things out. Use what you like

 

[PastryBaker]

I have seen inorganic like pumice work really well, as well as a fine sandy organic mix for thickening trunks. For trees in the ground, I like using inorganic for pond baskets and Anderson flats because the soil doesn’t fall out of them. For big nursery pots out of the ground, I like a sandy organic mix. Having a fine particle size is way more important than the mix for getting a fine root system when you are just growing things out. Use what you like
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Thanks so much. I wish I could plants in the ground, but out here it is not a good thing.

 

[Desert O'Piñon]

What is your garden/yard soil like? And what species are you trying to thicken? Desert soil is usually alkaline and often is also salty. Do you have sand, clay, or rock?

 

[Shibui]

Type of soil doesn't matter as much as how you can care for the pots and trees. It's much more about how you manage that soil. Inorganic can dry out quicker so if you are not able to manage watering well enough your trees will likely go through periods of drought water stress and consequent reduced growth. Inorganic mix also tends to hold less nutrient so need to be prepared to fertilise regularly to maintain optimum growth rates. Root problems caused by overly wet, organic soil will also be detrimental to growth and also set back growth rates. Many modern, open organic mixes also suffer nutrient deficiency without regular fert additions. All these factors will affect growth rates of your developing trees in pots.
I've seen great growth rates in both organic and inorganic mixes - and also problems in both.
Care, water, nutrition, etc are all far more important then soil components.

 

[Matt3839]

I have three cryptomeria, all bought in 2022. They were around 3 years old all similar heights and sizes of trunk. one is in a pot that got up potted a year ago, one in a pond basket, and the third started in a pot and got moved to a pond basket after 2 years.

The thickest is the one that stayed in a pot/ got up potted. The other two are equal thickness although the one that was always in a pond basket is about a foot taller and happier than the one that was transferred to a pond basket.

All three are in potting soil and pumice mix.

Not sure if it helps but just thought I’d throw that out there

 

[PastryBaker]

What is your garden/yard soil like? And what species are you trying to thicken? Desert soil is usually alkaline and often is also salty. Do you have sand, clay, or rock?

Sand and clay. and hard to plant in.

 

[PastryBaker]

I have three cryptomeria, all bought in 2022. They were around 3 years old all similar heights and sizes of trunk. one is in a pot that got up potted a year ago, one in a pond basket, and the third started in a pot and got moved to a pond basket after 2 years.

The thickest is the one that stayed in a pot/ got up potted. The other two are equal thickness although the one that was always in a pond basket is about a foot taller and happier than the one that was transferred to a pond basket.

All three are in potting soil and pumice mix.

Not sure if it helps but just thought I’d throw that out there

Thank you. Very interesting how they differ.

 

[MrBonsai19]

I would just add that you need to gradually increase your pot size so that the roots are always filling up more than half the pot. If you go to a large size pot like a 7 gallon nursery can but you have only a young sapling there will not be enough roots to dry the soil out properly and you will have issues. So even if the goal is thickening I would still gradually step up container size. 1 gallon -> 3 gallon -> 5 gallon etc.

I have seen Eric Shrader from Bonsaify talk about development mixes using 30% coco coir or fir bark plus 70% perlite. You could play with those percentages to meet your own requirements for flexibility in terms of watering frequency. 50/50 would probably perform just as well. If you had a deciduous water-loving tree (like a Japanese maple) you could go even higher.

 

[Wires_Guy_wires]

I second the 'less disturbance is better results' option.
I have stock trees in just about any soil, from bonsai soil in the ground, to ground in the ground, to ground in pots, and the key is to get the watering right.
The ones that do best, were planted over two years ago. The second best were planted a year ago. And then there's my junipers that don't do well at all, no matter what soil they're in or how I manage my watering. Those are going into year four or five without disturbance.

As for going up pot sizes, I agree with mrbonsai19: oversized is not great for rapid growth. Balancing on the edge of root restriction by limited pot size, is the way to go.
Adding a lot of bark though, did turn some of my plants yellow as the bark acts like a nitrogen and calcium sink. So try to feed accordingly.

 

[Sifika]

I would just add that you need to gradually increase your pot size so that the roots are always filling up more than half the pot. If you go to a large size pot like a 7 gallon nursery can but you have only a young sapling there will not be enough roots to dry the soil out properly and you will have issues. So even if the goal is thickening I would still gradually step up container size. 1 gallon -> 3 gallon -> 5 gallon etc.

I have seen Eric Shrader from Bonsaify talk about development mixes using 30% coco coir or fir bark plus 70% perlite. You could play with those percentages to meet your own requirements for flexibility in terms of watering frequency. 50/50 would probably perform just as well. If you had a deciduous water-loving tree (like a Japanese maple) you could go even higher.

Don't forget that he is running a nursery and is trying to combine saving money along with growing as fast as possible. There could be more optimal options.

 

[Desert O'Piñon]

Sand and clay. and hard to plant in.

Understood. Concrete is definitely not ideal for growing anything. However, if it drains well, and if you have the resources would it be possible to dig out a hole and fill it with a suitable substrate? Or is the hardness of the soil the reason it's unsuitable for planting?
It occurs to me that it might be beneficial to root development if the surrounding soil is too hard for them to grow into. Maybe it would have similar effects as planting on a tile in ground? This is just me surmising possibilities. I'm not suggesting to try this, but it could be an interesting experiment with seedlings, or with "excess" trees that you haven't put much work into. I would try it myself, but compacted sandy clay isn't the problem I have with the soil in my yard.

 

[Shibui]

It occurs to me that it might be beneficial to root development if the surrounding soil is too hard for them to grow into. Maybe it would have similar effects as planting on a tile in ground? This is just me surmising possibilities.

Filling a hole in hard soil 'might' also act just like any other pot, restricting root growth and tree growth.
Filling holes in hard soil with good mix can also be detrimental when there's water. The hole acts as a sump, filling with water which then can't drain away. I think most know what that means for roots.
I've dug up landscape trees that have never thrived after planting out. Usually find that the roots are still confined to the original pot soil and have not ventured out into surrounding soil. It seems that roots see a change of soil types as a physical barrier and continue to circle and grow in the soil type they know. There may be other factors at play. I'm just advising what I've noticed on several occasions.
Planting areas in hard or poor soil need to be large holes or larger areas of that soil amended to provide decent conditions for the roots to thrive. Raised beds of decent soil above the suspect soil is a great way to use space where soil is not great. If the original soil is really hard or not conducive to roots it may well act as a root barrier and promote that desired flat nebari. Just need to be aware that a 10 inch deep nebari grown in ground is no different to a 10" deep pot and nowhere near suitable for a flat bonsai pot. Root pruning will be needed on most root systems over 2" deep and the same root pruning will be needed as for root systems developed in much deeper containers. 2" deep good soil over crappy soil is unlikely to promote great growth so there are a great many factors at play when considering fast growing trees for bonsai.