You have a very nice tree Fred. You certainly have your own touch on the flowering species to make them beautiful and I love seeing them when you share, so thank you.
I have a contorted white quince and a toyo that have been in the ground growing for the last 3 years or so. I was debating digging them in the spring to either see if I think I can make something of them or to sell them off. I must admit I'm perplexed by how to style these as I really have only seen the clump style. I have to read the chapter in Peter Tea's book on them. I'm curious how you decide what direction to take them as from the little exposure I have to them, they don't lend themselves to a typical tree form. Also, how do they respond to heavy root pruning in your experiences?
The tree posted here is, depending on who's looking, either a single trunk or double trunk contorted white quince. With this particular tree, I let it grow for most of a season, and then made the decision to wire it so it would fold in on itself. Usually, I cut it back in early summer, and then let it grow until the fall, then cut it back again. I cut it to 1, 2 or 3 nodes, depending on design considerations. With this contorted quince, if I did that, I'd be cutting off everything that makes this little tree what it is, so I came up with the folding-it-back-on-itself idea. Now that I have a nice briar patch going, I will introduce another rhythm into the tree's growth, a little change of pace, but nothing drastic. So, in answer to your question directly, I let the tree tell me, on one hand, or I start with a bunch of cuttings to make a clump.
There are quite a few variations on the clump format. It's worth your while to look at some Kokofu books and other publications, like International Bonsai, which always (almost) has interesting quince pictures to look at.
Quince, according to the book, respond well to heavy root pruning, but I don't do it. The reason is that quince are susceptible to fungal issues. These can be devastating for the tree, so I like to have my quince as unstressed as possible. When I repot the quince, I take it out, check it over, and simply cut off roots that hang down. In the initial potting, I remove only what I have to. When I prune the branches, I seal the cuts. All of them. I use a couple different fungicides. With this regimen, my quince have really improved in health.
Thanks for your questions.