"I don't know how many annuals would work as bonsai"
Your right; not many annuals will work well as bonsai. Since the aspiration of the art of bonsai is to mimic trees on a small scale, the material used is also usually a tree, or at least a woody plant. So maybe annual bonsai shoud be called pseudo-bonsai. Anyway, the annuals in consideration serve our purpses well enough; they have small leaves and can, to some extent, be trained to resemble trees. My little begonias even have a nice beige-brown 'bark.'
"I don't have an exact measure, but I just measured a pop can and that's just under 5inches tall (pop can used for scale in the first post). I'm guessing with his new pot he's probably just that size."
Oops, I forgot about the coke can.
"I wouldn't call it training in the terms of wiring and branch shaping, as I can't wire this guy at all - the slightest pressure and it snaps. But it would be good for developing snip 'n grow techniques, and just for working on your 'eye'. That's what I'm treating this as, an exercise in design."
The design aspect of the training is exactly what I meant. Yeah, trying to wire these things would be pointless and, no doubt, very frustrating.
"he can go a day and a half without watering."
Ah, your impatiens appears to be less demanding than many mame. I hear of people having to water them several times a day. I typically water my plants with smaller pots once or twice a day. So you can save the greenhouses for the plants that really need it, and actually, the drier atmosphere outside the greenhouses probably keeps the leaves on the smaller side. Too much humidity tends to contribute to larger leaf sizes.
"I'll probably have to repot him twice a year if he keeps up the same amount of growth - totally pot bound from an initial June potting to Dec."
This accelerated rate of growth is a nice break from the usual length of time required for other bonsai, I would think
. I do wonder how long one can keep an annual alive, though...
Travis