Read this first.

Here is a link that might be useful: Soil discussion

I read it & I didn't like it, the information does not subscribe to my understanding of soil science. My compost is not a problem it has been sterilized.I seem to always have problem on this form, I don't know what the problem is. It is unlike all the other forms, haughty may be the word.

Having read the earlier discussion and choosing to go "your own way" based on your understanding of soil behavior and then criticizing others for feeling strongly as you do makes your postion or view no less haughty than theirs. So when you want help, becareful how you ask for it, or you might not get any at all.

But, on a kinder note, I'll put my best foot forward--most people don't work with sterilized compost so it is "commonly" viewed as a poor choice for and additive to maple potting mixes. Since yours is sterilized and you want to use it for moisture retention and nutrient supply then that doesn't sound so bad, but I would be hesitant to use as much as you are planning on.

Fir bark is a staple and I use 3 parts aged bark and 2 parts pumice. I have also taken to adding crushed red cinder to a few trial pots. That is it. I would think that the granite dust might be too small overall and as the bark ages you will lose air space. If you will repot frequently, then there does not seem to be much problem with your choice. I might use an ounce or less of the fertilizer, possibly only 1/2 ounce per gallon.

This is my first year using the mix above and I am finding that even near 80 degrees it dries out very quickly, but if I can get solid root systems with a lighter mix then I can increase moisture retaining compounds once the maples are in larger containers. I would think with 1 part compost you would have pretty good moisture retention if not too much in a wet season.

But honestly, if you have already mixed it, why are you asking now? If it seems good to you, then use it. Heck, everyone it an expert when it comes to maples--I don't know why we bother to ask qestions--we do as we want anyway.

Best regards.

And I would add that an "understanding" of soil science has very little bearing on growing plants in containers. Containers are unnatural, restricted environments often devoid of the natural biomass existing in inground soils and require very specific drainage considerations. An application of conventional soil science is pretty meaningless under these conditions.

You would do well to heed the information supplied by Al. He is inordinately skilled at container growth and the specialized conditions involved and is extremely well regarded for his very generous knowledge both on these forums and elsewhere.

Scheesch! If you'd only told me trying to help you required a subscription to your particular version of soil science, I'd have stayed home. Best of luck with your efforts.

Al (who's smiling broadly)

Personally I have used a mixture of of equal part kellogg's compost, play sand and peat based potting mix, For maples grown in 20" tubs it worked very well for me. I had a bloodgood and sango kaku and they have doubled it's caliper in size in 12 months. The sango kaku was 2 gallon still staked at the time, and the roots have filled out the tub competely, I took it out to plant it in the ground.

Maybe it is normal for these more vigorous cultivars to double caliper size in one year, but maybe not, I had another one in the ground and it has not grown as fast. I am in the process of trying this mix on the slower growing cultivars and dissectum too.

But, I think it sort of depends on what you want and your climate. For example, I began with an off the shelf mix that is very light but it requires watering once a day because it dries out so fast. The maple grew lots of new roots under a short amount of time.
But I can't really deal with the frequent need to water as I put the plant at risk if I miss a watering or two.

I had a similar experience with an osakazuki in a 25 gallon+ container: the mix I used was too fine (too much loam, compost, etc). After a year I changed the mix: the roots had completely invaded the container. That seemed all good. However, the tree had also developped a fungus (I discussed this with mjh a while ago). I suspect it was the mix (combined with a problem already present in the tree when I got it?). i guess my contribution/question is in how far can a disadvantageous mix be ok as regards growth for a while (a year), but detrimental in terms of encouraging disease?
I have followed Al, MJH and others' recommendation with interest, and they were priceless in terms of the info, and food for thought, etc.

H2O2 might help....

Well I have been search my Theseus as to what my attitude has been on this topic and the best one I found was supercilious. I am sure you are all correct about the soil mix for potting maples. It is as you say a micro-enviroment and does not apply to a field grown tree. Second with out your support my investments are in jeopard, you are the experts not me so thinks for the help. Now is growing Acers a guy thing like orchards are, I was a member of a local orchids club and to see a woman was a little odd, the only women there were the wives. Is that the same here? If it is mostly men here I could speak a bit more as I truly think, like ha sorry guy on the day I put in my jerko. post, I had just gotten a new hole drilled into my a. by my wife that morning for tracking in mud, so I was abit not all there, so I will try not to post when I am so pissed but I somtimes don't know how pissed I really am.