If the JM is in a pot it should be easily moved away from the sun in the hottest part of the day and later returned to your prefered display spot. There my be some seasons of the year where the sun is not so direct on the tree, so at those times the tree might not need to be moved away and back. About trimming trees. Please do some google searches for tree timming methods,and become very informed about the subject. In the meantime, try to find out which jm cultivar you have inherited. Hopefully it is a dwarf JM since it is growing in a pot. Other wise it may be a losing cause trying to trim it back within location size each summer. or after leaf drop for major pruning. Remember every cut you make affects the continued growth of the tree. So start slowly with the upkeep pruning first. Before any other limbs are trimmed, Use clean pathogen free shears. Prune out all dead or twiggy branches on the inside. Prune away any branch that grows into or crosses over another proper form growing branch. Your previous google searches should have yielded some good instructions on how to make the cuts. After those cuts the tree should look cleaner and opened up just a little better if it started out with a pretty dense canopy. As far as doing other trimming, be very stingy, because most dwarf or semi-dwarf JMs grow very slowly and any bad form timming done will not fill back in or grow back out quickly. It is my opinion that if you do not have a dwarf or semi-dwarf jm than move the tree to a proper light and adequate growing location.

Much better to move it rather than cut it back that hard. Cutting back by half is not considered 'trimming" -- in fact, it is not recommended to take any tree back by more than 20-25% at any given time. It is far too much of a stressor on the plant. And it is never a good plan to limit a tree to less than half its normal mature size - they are not shrubs - and even less of a good idea with a Japanese maple for a whole host of reasons. 12' is still pretty small for a 'Bloodgood' so perhaps a better location or a more appropritae choice is in order......unless you are willing to wait until it grows sufficiently taller that you can limb it up so the canopy is above the window. Wait until it is dormant to relocate or if too close to cold weather in your climate, do so in early spring before it leafs out.

tapla, I am searching out help in japanese maple bonsai and I noticed you suggested layering off the tree above the graft union. I have purchased two japanese maples ( at an excellent price for practicing ) and after reading this thread I went back and checked the trees for the graft union. In my excitement at the price I did not notice them before, but yes, the union on one of my trees is definitely visible and now that I can see it, it seems to not belong with the tree. Can I take the top off and root it with hormone, should I scar the bark, dust it with hormone and plant it with the graft union beneath the soil, thus letting roots form from the scion itself, and then remove the rootstock? Or is air layering the way to go? Assuming all this will be done at the right time of year. Which I have read, for maples is just before bud break. The other graft union is not so visible, so can I leave it or do you consider that the change in bark structure is detrimental to the beauty of the tree. Or will this union become more visible with time?

I would prune the dead and dying branches that are growing under the outer ones. They're going to eventually get shaded out anyway. I'd cut them off where they originate on the trunk. This results in a thin umbrella with a wavy edge, not a bowl cut. Do not cut any branches at their tips. If the branch is 'too long' cut it off where it begins, not just short of where it's touching the ground. You want to show some of the curved trunks that is now hidden by leaves. That's one of the prime attributes of this plant and should be partially visible in the summer as well as the winter. I always say, "If ya got nice legs, show em'!" Your maple should be center stage and the shrubs on the right in picture one should be moved to the wings.