I’d like to start a thread to discuss the various components we put into our soil mixes. This is probably different for everyone so I’m not looking for recipes but rather why you use each of the components, such as perlite, vermiculite, lava rock, sphugnum moss, sand and of course the elephant in the room akadama.
I’m just interested to find out what each offers and how to start experimenting with a soil mix that would suit my tree’s as a general mix and then maybe delving deeper into something that might be more suitable to conifers and deciduous.
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From your list:
perlite - I use this for cuttings and as a part of basically every “in development” soil mix. The reason being it is the absolute cheapest component that is good at holding air / water.
vermiculite - I’ve tried using this for cuttings but no longer use it for anything
lava rock - I’ve used this for years, but am wondering if its worth it anymore. Its a part of the trifecta of 1:1:1, but I’ve heard some recommend that just pumice / akadama is every bit as good. I will be doing some tests on that someday when I run out of my current stash.
sphugnum moss - air layers and top dressing
sand - I dont have a source for the “sharp sand” mentioned in naka’s books, and regular sand is not generally a good idea for aggregate mixes
akadama - hey it works. I dont use this at all for trees in development, but I do use it for nearly anything in a small pot.
Others:
Pumice - This is like perlite that doesn’t get crushed or float. Imo its the best all around soil component for almost anything. Its a bit more expensive than both perlite and DE, so I use a bit of each in development mixes to stretch the pumice out. If I had a cheap source of bulk pumice I might use 100% pumice for quite a lot of trees.
Diatomaceous earth - Ryan did some experiments with this and didnt love it, but I’ve had good luck with using it as one component in mixes of trees in development. This is the next-cheapest component after perlite.
Shredded coconut husk / pine bark - I used to use one or both of these to make my mixes more water retentive and try to make up for the 100 degree summers here. After a few years of testing, I am no longer convinced it actually helps noticeably with water retention or at all.
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Thanks for this great list. I’ve also been seeing something called Cation exchange capacity(CEC) which also seems to be something important to take into account for each of these.
From what I’ve read perlite has a CEC around 0% whereas pumice around 10-20%. I remember Ofer Grunwald saying that he uses Vermiculite to help with fertilizing and this could be the reason. I will ask him again when I see him. So it could be that this is something to take into consideration when building up your own soil mix…
Unfortunately I am away from home quite a bit so I have an automatic watering system, a drip system. Not ideal but this is something I need to work around in terms of a soil that can hold onto and maybe also distribute the water efficiently. We have zero summer rain so this is also something I have to think about.
I can add a bit more perspective on components I use for developmental work with a focus on CEC and water retention. I started experimenting with different blends to see how they affect development a few years back on slash pines, italian stone pines, southern live oaks, and some bald cypress. Here’s what I’ve found.
TL;DR: Use organics with either pumice of lava rock for fast trunk development.
- Coconut coir - I add this to really ramp up developmental growth on species that love wet soil. The coco has good CEC, lower PH, and retains water like nothing else. Note that it does need something called buffering where you have to really hit it with CalMag or it won’t properly release nutrients. The bald cypress and slash pines love this stuff so long as it’s paired with something to prevent compaction.
- Pine bark - I add this to species that need lower PH, but more air in the roots. Like the coconut coir it has a high CEC, but because it comes in chunks it naturally provides better aeration and holds less water. Stone pines seem to respond well to this with pumice.
- Horticultural Charcoal - I’m experimenting with this as an substitute for organics in species that like almost no moisture. From what I’ve read, it’s CEC is comparable to organics, but it doesn’t hold nearly as much water. It has a neutral PH, which needs to be offset. I’m trying it out with a Joshua tree.
- Kanuma - Everyone talks crap about this stuff, but I think it works just fine with my pines and really brings down the PH. I started adding this to my slash pines when they all started showing signs of yellowing and haven’t had issues with them since. I primarily use this just to regulate PH levels.
- Akadama - I stopped using this for trees in development. Akadama is great for refinement, but if you’re looking to put chonk on a trunk, I’d save your money and replace this with organics. The trees I have grown with organics in place of Akadama are about twice as thick as those grown in Akadama blends.
- Lava Rock - I use this in place of pumice for trees in development that like a lot of water. Like pumice, it keeps the soil from compacting, but all the tiny holes in it hold on to more water.
- Pumice - Good old pumice. This goes in pretty much everything to avoid compaction and add a bit of water retention.
- Peat Moss - I stopped using this altogether. Initially it does add really good CEC and low PH, but after about a year, this stuff compacts into a sponge that pretty much chokes roots and encourages algae.
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Thanks so much @bentleythekid and @chitown_bonsai
From what I can see from your feedback and actually something that I have seen on another bonsai grower in Oz is that organic when developing is a really good way to get the tree growing.
I’m actually planning on trying out growbags and then using the information you provided to see if I can come out with a good mix.
I also saw the propagation video and he was using pure perlite for the cuttings so will give this a go to. Might make getting the roots untangling a bit easier.
I’ve been using grow bags for a couple of years now and they do work very well for encouraging fine root growth. Some things to keep in mind though are that the roots will actually tend to grow towards the bottom half of the bag since the top dries out much faster and that fabric bags will grow all sorts of gnarly moss/algae on the sides which can inhibit air intake. I haven’t quite figured out those issues yet, let me know how it works out for you.
I was thinking of burying the root bags half way and then mulching the top half, even mounding it up a bit more. I don’t think we’ll have a moss or algae issue here just due to the fact that it’s so hot here. My main issue now though is sourcing grow bags here in Israel. I’ve tried contacting the Rootmaker site but haven’t heard anything back from them. Might try making my own if I can find the right type of fabric.
I buy my grow bags on Amazon.
They are made from non-woven geotextile fabric.
If you have a serger sewing machine and can source the fabric in Israel you can definitely make them 
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I use bags made of a felt like fabric and they are working well, you can use burlap sacks as well you might have them in the form of onion/potato bags?
Take a listen to the Telperion farms episode of the Mirai podcast. They discuss substrate and are renowned for the quality and speed at which they develop their trees. I believe the substrate is a mix of pine bark, pumice and manure. I have just popped some trees in the ground using the same(ish) mix and they are doing great so far.
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I there!
This is quite an issue and it feels there is some trends over the years. Were I live in mediterranean Spain I’ve seen different mixes in Youtube and they have been shifing overtime.
Over here nobody talks and sure most of people do not use the 1-1-1 lava-pomice-akadama, in fact lava is not mentioned. If so I’ve listned complaints about it being very abrasive when removing it on repottings.
The most will use Pure Akadama for more water loving species and some sort of mix with pumice 2-1 - 60/40 - 50/50 (here Europomice quite affordable).
Also was pretty popular 2 AKA - 1 Kiriuzuna, specialy for pines they argue kiryuzuna is a bit acidic.
I’ve used 100 pumice in yamadori material.
With the covid crisis people tried with crushed ceramic bricks and also a cat litter soil (katadama) but i can’t tell.
I will add Aspen wood chips… animal pet bedding (bark shavings). I use it for collected trees and any tree that needs rapid root production in a single season. This was based on the Randy Knight recommendation and I have done it for 3 years.
species dependant I will add 1/4 perlite and mushrooms compost. This is also the mix I use for anything I have in grow bags or development. Which is 60% of my trees