Whilst all of the points raised previosly are valid to a certain extent, there is one critical factor that has been overlooked and that is the compost. In the wild, maples get 7 to 8 in. of rain a month during the summer and grow in free-draining volcanic soils. Replicate that and you can happily grow any Japanese maple in any size pot in full sum and in temperatures from -20 deg. c to shade temperatures of 35 deg. c without any damage providing you start with a healthy plant. As this is my first post I've kept this message short; hopefully this post has been made correctly. If you would like me to expand on the above, I will be more than happy; I speak from a small amount of experience as a commercial propagator and grower of Japanese maples for the past 25 years.