I agree with Richard that the pots look too small. They should be okay for a year, perhaps two, then you'll need to re-pot them.
Are the roots growing out the bottom of the pots they're in now? That's always my cue to move them up. Five gallon pots move easily up to fifteen gallon pots that aren't completely full, leaving 6-8 inches at the top for a good mulch. The fifteen gallon pots fit nicely into pretty pots that will give them some protection from pot sunburn. When they start growing out the bottom again, it's easy to slip them out, add more soil at the bottom, and slip them back in again, this time filling the pot to the top. But I have a lot of fifteen gallon size pots so it works better for me.
I read or heard somewhere that trees really don't go completely dormant here in SoCal with our warm winters. The leaves fall (usually) and the tops look dormant but the roots keep growing, albeit at a slower pace. That way the trees benefit from all our fall/winter rains and softer soil that doesn't freeze.