I screen mine through aluminum insect screen & use everything that doesn't go through. I'd guess that about 1/2 - 5/8 of a bag of MVP is usable in soil. The fines are great for very small (mame) bonsai or used in hypertufa troughs as a replacement for sand.

Al

That's excellent advice. Turface is a good product to replace pumice in your mix (or sand). It holds moisture some and will never break down. Soil particle size is an issue in bonsai because of water retention properties. By and large the bast majority of homemade and purchased bonsai soils are far too fine and hold too much water for most trees.

I use a larger mix than that for all my trees. Deciduous and water-loving evergreens like Japanese black pine get particles about 1/4 to 3/8 inches above the drainage layer. Alpine conifers like Japanese white pine, Scots pine, Mugho pine, and Colorado blue spruce get a far larger particle mix, 1/2 inch and up.

Grading the particles like this means I must water more often, but I do work 50 hours per week, and my automatic sprinklers water every tree the same. So the trees with larger particles keep less water and the trees with smaller particles keep more. That way I don't have to remember to water this one every day and that one every other day, or that one once a day and this one twice a day. Life is much easier.

Chris

Here is a link that might be useful: Inorganic soil mix

It holds moisture some and will never break down.

That isnt particularly the case. Turface will break down. Its a fired clay that will usually last the 1-3 year repot cycle but by that time you'll be seeing that the Turface is breaking down. I'm sure theres some locale-specifics involved, but I've got a boxwood (nothing at all to look at) that needs repotting and its in a heavily-turfaced mix. There are just starting to be signs that the turface is not without an aging process. (Admittedly I should have repotted it last spring but its in a sufficiently oversized pot I thought I'd let it grow/go.)

To the OP... screen it first. There are a lot of fines in it that won't be doing your trees any favors.

I use 100% profile on some of my plants. The manufacture stats 'decompose by 3.5% in twenty years'. I have not yet seen the decomposition yet. However I use profile and not turface, which from what I understand are the same thing but the manufacture does not list composition on turface as it does profile. I have mixed it in with my soil and the soil stays damp longer, not wet.

Thats my 2c on this old post.