tldr; can I effectively trunk thicken by putting nursery stock in extra large containers filled with akadama, or am I better off using potting soil?

Hi!

I’ve recently discovered Bonsai Empire on youtube, and firstly, thank you for the phenomenal information that you present!

My question is related to developing pre-bonsai material in akadama. I understand that develop is fundamentally different from refinement (in that tree shaping is secondary, and critical growth is primary).

Specifically, I have a few pomegranates, olives, and an avocado in 6” nursery pots that I want to develop, especially in the trunk. While I’ve researched the techniques of sacrificial branches, wild growth, trunk chopping, etc, I’m not at the point to employ any of those yet. One popular technique is to ground plant and come back in a few years, but I live on the sixth floor of a downtown apartment building, so that avenue is not available to me. What I have instead (and this guided my tree selection) is a huge south facing window that runs about half the length of my apartment and gets blasted by the sun. I estimate that if I pay attention to the appropriate factors, I can get fairly rapid trunk thickening if I up-pot to containers large enough to mimic the uninhibited barriers of garden planting. After all, the small containerized environment is the single largest factor in all but halting the growth of bonsai.

Therefore, my exact question is whether I should repot into akadama soil, or in potting soil?

My understanding is that the nutritional content in potting soil depletes fairly quickly, and balanced fertilization will be necessary early on regardless of the soil medium. But by starting in akadama with fertilizer supplements (after an adjustment period), I suspect I would gain the benefits of better O2/H2O balance, and the rod structure of the clay would promote fine feeder root developments which in turn would promote fertilizer uptake, canopy growth, and ultimately vascular growth.

For reference point, all three species grow in similar soil types and conditions - loamy to sandy, fast draining, and soil pH 6-7. Their water needs are slightly different, but all thrive in bright, full sun with mild to moderate humidity. The soil mix I intend to use is 40% akadama, 25% perlite, 25% lava, and 10% orchid bark (by volume). I plan to include the orchid bark for two reasons: cation exchange capacity and soil pH reduction. The fertilizer I plan to use is a slow release 6-8-10 NPK. I also have a sheltered balcony for winter dormancy concerns.

I would appreciate any guidance you may have.

Thank you,

I use akadama for all my potted plants. Herbs, flowers, cactuses, and of course bonsai I use akadama because I live in Japan and its available at every gardening shop, and its cheap. If I move back to Europe, or wherever, chances are I quit using akadama, and switch to something I get at my nearest gardening shop for a cheap price

PS. Some of my prebonsai are in my backyard, which is mostly some kind of sticky muddy clay, and some are in big pots, which contain akadama and something else (soil from my backyard, compost, sand, whatever).

No matter which substrate you use, you will have to fertilize.

I do not use akadama. Do not like the stuff. For growing out, I use my regular substrate if in pot, as that allows me more control over water, and I do not need to worry during the 4 months per year where it sometimes does not stop raining for weeks on end.

I am getting away from akadama. It breaks down and requires repotting too often. I want to repot when the tree wants it, not when the soil wants it.

Leatherback, if you don't use Akadama what do you use? I was thinking of using a mixture of Turface, crushed granite, pine bark and lava rock. (I also wanted to add a small amount of Sphagnum peat moss) for my Bonsai. I am new and still trying to put together a mixture. I know I will need a couple depending on the trees.

I live in the states, Philadelphia Pennsylvania. Some bonsai trees that I am going to repot in the spring are Japanese maples sweet gum tree, dawn redwoods, juniper, and spruce,.

I am looking for any advice.

Thanks

I use an expanded clay which in Germany is called Blahton, with bims (pumice), pinebark, lava, zeolith and some baked clay. Mostly because I re-use my substrate and thus different new batches get mixed in with the old.

Read my ideas on substrate here: www.growingbonsai.net/characteristics-of-good-bonsai-substrate/

Thanks, Leatherback!
This was helpful!!

My experience is roughly the same as Leatherback, except that he is a couple of years ahead of me. It's great all summer and in winter turns into mud.

The indoor trees I reported three years ago are doing great. The outdoor trees last spring are mud. I experimented with my wife's spices and got the same experience.

I plan on using up akadama I already have with indoors and going to mostly expanded shale or something like that, trying to catch up with Leatherback.

There is a lot to learn .
Now if either one of you could give me any Advice on fertilizer for the plants I listed above that would be a bonus.
If I follow what I have been reading I am going to have a different fertilizer for each plant.

Special fertilizer is a myth and good business. I just use what I have awailable. The sheaper the better. High in nitrogen most of the year and high in phospor in authum.