I moved both. They did not like the 90 degree days. My other spots are a bit too shady but they’ll prefer it there until October.
You'd be surprised how much shade you can create like in this corner of my otherwise blistering deck. Top rail is a 2x6 but mitered corner...
I like your grow box. Are you letting them live in those for a few years? What kind of maintenance will you do on those?
Well the grow box has a silly plywood bottom that won't last. It's actually a drawer I had made from Aspen for the kitchen bar.
The maple is planted on a 6" round saucer for nebari, and yes will be allowed to grow out and chop back perhaps each year IDK.
I'm learning maple development as well. I did build one grow box this Spring that took ~12g of bonsai soil along with a mountain maple I lifted
that had been in the ground for 10 years. Here's best advice I can give on such. Dig up or lift or repot, and tend to the roots to condense the root zone.
Had I been doing this with the tree I lifted, I would've had feeder roots closer in, and probably used half the soil I had to.
Now, the nebari would look better with root grafts...in time. Years wasted...
I've ruined more than 1 project by simply letting them grow unchecked, both topside and below ground. Grow out cut back, repeat.
Peter Adams has a book on Maple bonsai that's helpful too, but nothing replaces experience.
Shirasawanum is never near as robust or hardy and responsive as Palmatum. Green forms typically hardier.
I have a grafted Autumn Moon in ground 10 years as well that I've began layering on the top. I would like to lift it
but will learn care better before I do, and get a couple successful layers taken hopefully.
You may not be concerned with the graft, and that's fine, especially if you grow it out and layer from it
However, most likely, the root stock will out compete the cultivar, more and more as time goes on.
I'd get hooked up with Brent in the previous link and get a few cutting grown cultivars. Learn/experience in a few numbers rather than one or two.
Get one in the ground a few years...keep it alive.