Best type of soil for wooden growbox

Hello Mirai community.

My plan for the oncomming spring is to put an acer air layer into a wooden box.
My question is, what soil type is best to use to promote as much growth as possible.
is a 1 : 1 : 1 akadama lava pumice ok, or are there better alternatives like only use pumice?
i find alot of soil mixes for refinement, but nothing for much growth.
I know that placing it in the field is best, but that is not an option. :sweat_smile:

The plan is to grow primary branches since there are none of them on the trunk.

I live in Belgium.
Thanks in advance.

PS: sorry for any spelling mistakes :smiley:

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For getting growth, a 50/50 mix of pumice and bark or peat or other organic.

I use that on all my air layers after separation.


Thanks for the reply.
I forgot to mention that, this air layer was separated in september 2019. I have put it in a plastic container, and let it rest for a whole year. Must this be treated differently than immediately after separation?

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That doesn’t change it for me. In my experience, if you want rapid growth (no matter how recently it was separated) , pumice and bark is a good mix for aeration and nutrition.

Once you start adding akadama, the growth slows and that starts the refinement process.


+1 for the pumice and bark approach in the grow box. Provides good balance of o2/h2o as well as aides the aim of the grow in grow box.


what am i missing if i use straight pumice?


Cation exchange capacity is dismal in pumice.


Per B. Bentley - If CEC is lacking (which a pumice as pure SiO2 would be) adding some horticultural charcoal or bark or both would likely help.


I have heard of the cation exchange capacity to be low on pumice. But it aint zero. Despite the low score, I havent experienced any bad effects of using pure pumice. Im actually cutting back, about half way, how much I fertilize this year because of how much my trees have taken off. I work with mostly yamadori and the trees in nature have even worse soil conditions.

Maybe it is because I insist on using only liquid organic fertilizer. I think there may be room to explore and experiment in the efficacy for pines by using pumice and liquid organic fertilizer

I wasn’t saying that you’re doing it wrong. You asked what you’d be missing with 100% pumice and as far as I know that’s it. Well, that and scaling of the roots. I also use 100% pumice and fish emulsion in my yamadori boxes. :man_shrugging:t4: No way of knowing if a plant would do better with organics without experimentation. My area is so humid that I didn’t feel the need to add bark compost to the mix. I think I may try it in one or two of the boxes I have planned this spring. We’ll see.

This year I’m going to experiment with chemical ferts in my yamadori boxes. Specifically Dyna-Gro Bonsai Pro. I’ve used bio-gold in my yamadori boxes last year. I didn’t like the way it caked up at the surface. It broke down faster than it broke down on my bonsai pots though, so there’s something to be said there I guess.

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If the CEC is lacking with pumice, can it be replaced/added in the soil mix with zeolite?

Interesting. I’ll have to see how that compares to pumice in terms of price. Does zeolite make the water readily available like pumice? If you want to add a nutrient component I don’t think you can go wrong with a type of bark. I’m using pine bark this year.

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In europe, i can buy zeolite for almost the same price as the pumice.
I have found this shedule a while ago, Bonsai compendium - Google Sheets
i don’t know that it makes the water readily available, but looks like it has a lower water retention.

i also do not know how accurate this shedule is… :sweat_smile:


There was a good thread on zeolite a few years ago that is maybe worth revisiting.

IIRC Zeolites aren’t readily available in the US but maybe there are some sources out there.

Before getting into bonsai, I got some of this zeolite mix for houseplants. It was pretty good, but maybe a bit pricy (especially compared to garden center soil) so I stopped buying it but worked well. Every so often I think about buying another bag just to see how it would stand up with bonsai.

From the website the mix is:

  • Zeolite
  • German washed pumice
  • German, light Lava (permanently supplies your plant with iron)
  • Fully-coated, premium-quality fertilizer.
  • The coating is purely organize and breaks down without leaving any residue.
  • The fertilizer supplies your plant with nutrients for up to 6 months.
  • Fit for all plants, including foliage, flowering plants like orchids, citrus plants, herbs, tomatoes, fruit trees, cacti, and more.
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I purchased plants from Meehan’s nursery once. I asked them what they use in their mix. They said perlite, bark, haydite and turface. The roots this mix produced were pretty fine though.