A number of people advised me to repot my ponderosa as soon as I reasonably could: I live in a wetter part of North America than the tree came from, with at least twice the average annual precipitation. Andy Smith's mix is formulated for his climate out west, and would hold too much water here in mine.
The tree was healthy, so I did it on March 9. That was early -- we've had snow several times since -- but ponderosas are very cold-hardy, and I didn't want to make the same mistake I made with several pines last year. I didn't repot until the end of May (partly because of being so busy,) and by then most of the spring growth flush was already over. The trees' roots systems were never able to recover sufficiently. Among the trees I lost as a result was a very nice bunjin
Pinus sylvestris (Scots pine.)
I used a nice, roomy growing box partly because I didn't know where the major roots ran, and partly because the tree is still adapting to my climate and a lower altitude; I wanted it to be under as little stress as possible. The inside dimensions of my home-made box are 9 inches by 12-1/2 inches, by 3 inches deep. (Sorry, I'm not sure of the metric conversion.) The bottom is hardware cloth with a 1/8-inch mesh.
The largest surface roots arise in one small area of the base, and run fairly close to each other; they must have all followed the wide crack in which the tree was growing in the wild. Imagine that you are looking down at the tree from above, with the movement of the trunk pointing to 12 o'clock on an imaginary clock face. The major surface roots all grow in the direction of the area between 2 and 3 on the clock face. That is on the side toward the chosen front for the tree, which is fortunate because I'm not going to be able to do much to change the nebari. I'm going to have to find a way to incorporate it in my design.
I used the soil recipe that Andy described at the workshop: 50% Turface, 40% grit, and 10% organics (in my case, composted bark.) Other ponderosa-bonsai growers in this part of the US use no organics at all, but I decided to follow Andy's recommendation. All the ingredients were sifted, and I used only particles between 3 and 4.5 mm.
I de-wired the tree at the same time, and some of the branches have since reverted, at least part-way, to their old positions. Once I'm sure the tree has recovered fully from repotting shock, I'll re-wire.
I've managed to protect it from sub-freezing temperatures since I repotted it (with the exception of one night.) Yes, ponderosas are hardy, but again, I wanted to minimize stress as the roots recover. It seems to be doing as well as I can expect, maintaining healthy color in its foliage.
Here are a few pictures.