A fellow EasyBloomer wrote in asking...when is the right time to prune and transplant a Japanese Maple? The best time to prune a Japanese Maple is when the plant has gone into dormancy and all of the leaves have fallen off. This usually occurs from late autumn to mid-winter. In more Northern climates this can happen even earlier in the season. The reason why you want to prune when the leaves have fallen and when it is dormant is because you don't want the maple to "bleed" much. Japanese Maples are scientifically known as Acer palmatum. Their close relative is Acer saccharum, aka the Sugar Maple, which is also famous for "bleeding". Of course, we enjoy the sap from a Sugar Maple as maple syrup. Luckily most Japanese Maples don't need much pruning. If you want to train it into a tree, you will have to remove competing branches to maintain a single leader branch that eventually becomes the tree's trunk. Also, you will want to maintain a healthy architecture within the canopy of the tree. If you have a secondary branch crossing through the inside of the tree, you should remove it. Luckily, with all the leaves off of the tree, it is easier to see the architecture of the branches to see where to prune. You also might find some twigs on the main trunk or branches that you can snip off.
As for transplanting, I would do this also when the tree is in dormancy. When we transplant our plants we put them through a lot of shock. It's usually a good idea to do this when they're dormant. It's kind of like going into surgery. I know personally I would want to be knocked out for the procedure. Consider the plant's dormancy as being put under by anesthetics. :) I hope this is helpful. Let me know if there are any questions out there. Cheers...Robby