AusBonsai

Hi Brett,
I have just read through this post and some of the linked material, like many I missed the poll (and the initial post).
It is a hard question to answer, so many different genus, so many different environmental variables (even within Australia), so many different experts, so many different opinions
One point that you made about drainage in relation to size of the hole in the pot, air circulation in the pot is part of the reason for the hole size and is worth considering in relation to health of the tree, but then we should consider at least the differences (of which there are more of) before potting.
Personally, I like to do a little tailoring of soil for each type of tree, even species.
I am having good results with 2-7mm pumice straight or mixed with aged pine and/or other ingredients
Happy Christmas.

Yes Damian, I thought many are using the 2-7 mm and getting great results but I wanted to propose the idea of using smaller and much the same size medium. My belief is that when a tree is in a more refined state as far as roots go at least then they will benifit from a more refined soil. Say 2-4mm

Bretts wrote:Yes Damian, I thought many are using the 2-7 mm and getting great results but I wanted to propose the idea of using smaller and much the same size medium. My belief is that when a tree is in a more refined state as far as roots go at least then they will benifit from a more refined soil. Say 2-4mm

Hi Bretts, anything to do with potting medium is like discussing a pretty girl mate. Everyone will agree the girl is pretty, but everyone in the conversation will have a different reason as to why she is pretty. On this ocassion you and I agree with the 2-7mm size grit, when you can get it. I also agree that older, closer to finished Bonsai are better planted into a mix using a smaller grit, indeed I believe with really older Bonsai, the grit could actually be left out all together, but only the very old Bonsai and for nothing still undergowing anything resembeling training.
In my own mix I use a grit which will pass through an old 1/4" mesh screen I have but is retained by a 1/8th" mesh. I'm old, so will let you do the conversion maths. I have nothing in my collection which is anywhere near old (in training years) and everything I have goes into the same basic mix.
At the end of the day, the best mix, or components of the mix are those which will work for you in your situation, it's how you get to that conclusion that sometimes draws the issues hey.

Even now I am sure I still have lots to learn about potting soils. I don't think any one soil is a best fit for all scenarios.
Another point is how long between there are so many variables that you just have to put alot of energy into understanding how they work.
No wonder Bonsai is the pinnacle of horticultural achievement

Did someone mention roughness or surface texture of bonsai soils or was it in one of the links?
It may have been in a link and was relating to an opinion about roots spreading when they hit sharp/rough particles. The preference was toward akadama/kanuma being the best, I have to say that a lot of personal opinion on this product is not that hot in Victoria (keep in mind, this is Victoria I am talking about ). Due to this I gave pumice a go and I was pretty happy with the results. Not just for its ability to allow water and air penetration but also for its reusability. I think it was the first link, the writer was rating the Japanese soils at the top but she also mentioned that they break down after a while.
Pumice does not go soft, therefore it can be sieved and reused over and over providing you take some precaution.
Perhaps materials in the US differ greatly from those available here

Good thoughts Damien,
I think the thing about roots splitting when comming in contact with sharp edges is widely excepted as a myth. I still prefer sharp edges, it at least seems to create better spaces. These better spaces [layman term ] would create better finer roots and hence you can see how these sought of myths start.
And yes considering akadama is considered widely by masters around the world as an excellent if not the best medium to grow in {at least for trees that are repotted every few years} you wonder why these people who have only just started using the product don't look to themselves as the issue instead of the akadama.

I have been using 2-7 mm grit, and have had troubles with parched trees (esp. this year) over the hottest bit of summer, and I'm thinking of going down too 1mm as smallest particle size in my soil. We have had regular days over late-December/January/February of high 20s to low 30s, only now with the shorter days are my trees starting to looking healthy again.
In one of Colin Lewis' books (I can't remember which, and probably in more than one anyway), he says to use smaller particle size to retain moisture better, as opposed to more organic material. I'm not sure how that would fit with older trees, as their growth rate is slower and transpiration rate would ( ) require less water, and the soil would need water-retention less than for a more vigorous tree. One of many factors to be considered, I suppose.

Over the past 6 months I have been using Mt Sylvia Diatomite (Kleensorb). I don't sieve or clean out the dust.
My mix is roughly 70% Diatomite (2-7mm), 20% 'Premium' potting mix, 10% Perlite.

Compared to my plants potted in 100% 'Premium' potting mix when I first ventured into bonsai, and the more recent stock planted into my own mix, the root growth is phenomenal! The water retaining ability of diatomite means I only have to water once a day, even during mid-summer in the high 30's. This goes from plants growing on in styro boxes to those in shohin pots. I've just collected a Ficus Obliqua a week ago, only managed to get 1 root without feeders, and already have roots extending 2 inches.
I also collected a heap of Casuarina seedlings, half when into my own mix as a 7 plant group planting, the rest went into the ground of a 100% premium potting mix. 4 months after collection I can say the top growth of both groups was very similar, though the root growth and development of nebari's was much more pronouced in the diatomite mix.
So in conclusion I prefer a primarily non-organic mix. Kleensorb claims to be 2-7mm but I don't go to the lengths of measuring and sieving. I just go by the look and the growth results really speak for themselves. I must also state that during the growing season, I mostly fertilise weekly. A rotational basis of Charlie Carp, Yates fruit and flower, and one of hortico's fert's. All along with osmocote slow release for citrus fruit (received at repotting time), and selected plants get dynamic lifter.
An added bonus of diatomite is no nasty's getting in the soil and potentially damaging the tree

sorry to ask a question out of subject, have any one of u heard about ceramic granule or granile. i ve come across that and the lady at the nursery told me it can be use as decorative on the top soil for pot or also used at the bottom of pot for drainage. a search or the net did not provide much info but it is mention on some gardening site. can someone please enlightened me

coomy20 wrote:sorry to ask a question out of subject, have any one of u heard about ceramic granule or granile. i ve come across that and the lady at the nursery told me it can be use as decorative on the top soil for pot or also used at the bottom of pot for drainage. a search or the net did not provide much info but it is mention on some gardening site. can someone please enlightened me

Coomy, I've never used it but it seems like ceramic granules should work as she said. As a drainage layer, you just want something that drains fast and won't break down and ceramic should do that just fine. I would look for a larger size if using for a drainage layer, say 6-10 mm?

Regarding top soil decoration, that's not something I personally would worry about unless I were showing my trees (and moss is traditional for that). The only exception would be on really hot days, if the soil is drying out you could put something moisture retaining on the top soil to prevent some evaporation. I don't think ceramic granule would help for that though.

Depending n the type of ceramic, it might actually have a little water retention capability, but I'm not sure about that. Would be interesting to experiment.