Gnome, thanks for the tips. I noticed an auto-parts store the other day that I'm pretty sure is the right one for those chunky DE.
You're welcome. It's funny you mentioned NAPA D.E. I just bought a bag of it the other day. I have not actually used it yet but from reading others experiences and knowing the actual composition of the product (FLOOR-DRY #8822) I am confident it will perform as expected. I had to sift it of course and not all of it was suitable but it was only about $8 for 25#
I'm leaning towards some organic content so I have been thinking screened chunky DE and small bark mulch mixture of some kind... I'm thinking I might start a bark/wood chip compost for the purpose.
Don't confuse soil-less with inorganic. The majority of my pots, although soil-less, contain an organic component, which for me is aged Pine bark. Look for a product such as soil conditioner as it is already partially composted. If you can't find such, get a big bag of Pine bark nuggets. This material is almost always too big but you can usually find some smaller particle in the bag or you can break it up without too much trouble especially if you only need a little. Whatever you don't use can go into your special bonsai compost pile for next year. Remember consistent particle size is what we strive for. The best draining mix is one that is composed of similarly sized particles throughout. The concept of a drainage layer is largely discredited. Similarly, it is important to remove the native soil form the plants or you will have two zones in the pot, one more water retentive than the other.
You can also use Perlite if you can find some that is not too fine. Many growers don't like the looks of this and some will float at the first few times you water but for plants in development I don't mind the obvious white particles. Lava Rock is another excellent component but you probably won't find it in an appropriate size unless you go mail order. Our member Tom (Tachigi) offers this material, and others, if that's the route you want to take and you have the time to acquire it.
For the Rose of Sharon in the ground, should I cut off its tap roots (meaning the roots below the shrub)? I only cut straight down in a circle. Should I do the cut off, up-root and "tile" thing and then put it back in the ground? I could do that too.
My practice is to dig the plant. wash the roots with a garden hose and then prune. This gets all of the garden soil or clay particles out allowing you to get a better look at the root structure. It is also easier on your tools. Yes, prune the tap root back. Use your judgment to determine where to cut. If there are a lot of roots near the surface you can be more aggressive and still expect a good outcome. It could go back into the ground, a lot depends on your goal.
We often suggest field growing to thicken young stock but your material all seems to have some girth. Besides, if you wanted thicker trunks you would have let them grow more before the first chop. Since you chopped them I assume you are ready to start refinement. Of course you can prune it and put it back into the ground on a tile. There's more than one way to approach this.
Oh! One more thing -- I love the radiating symmetry of the roots in first photo. Is the difference between the two due to naturally developed -- as in rooted cutting or a seedling vs. pruned off thick roots?
They are both seedlings but of differing ages and species; the top plant is younger. The bottom one may not have been worked on early, or aggressively, enough so I had to go backwards a bit. Actually you want a little 'thick root' close to the trunk as this will later become the exposed nebari.