Drill additional holes in the sides, near the bottom. If it has been in that mix for awhile, the mix may be becoming old and mucky - providing the basis for your concern. It will have to be re-potted to solve this, to avoid wilting you merely have to wait until it is leafless and do it then.

Thank you! Went to my nearest big box store and bought a drill bit made for glass and drilled 4 holes into the pot. It was like tapping a maple tree....pun intended. As soon as I made it through the pot with the bit, water just oozed out...so my tree was probably being drowned. (If you try this yourself, I used the largest Bosch glass drill bit and a hammer drill (made for drilling into tile.) I am sure the heat had something to do with the leaf loss, but now I am guessing that the swamp conditions were the main culprit. Thanks for the advice! :)

Added drainage holes will help but you really need to do something about the soil. That mix of ingredients will not be of benefit to your tree longterm and eventually will breakdown and compact and create more aeration and drainage problems than even additional holes will solve. No topsoil, no garden soil, minimal compost (just composted bark) and no soil products produced by Scotts/MiracleGro.

Try checking out the attached link from the Container Gardening forum. It is the eleventh posting (representing several thousand responses) to a small "treatise" on container soils written by one of the most knowledgeable container gardeners I know. Follow his advice - what you need to consider is the last recipe listed, or the "gritty mix" - and you can't go wrong growing anything in containers.

Here is a link that might be useful: Container soils - all you need to know :-)

Japanese maples are quite prone to impeded drainage, you might want to get it out of the mud before autumn leaf drop.

I've been trying Miracle Gro potting soil in recent years and doing pretty well with it, overall. Since it is a soilless mix I don't expect it to last for a long time.

Got it out of the muck and replaced it with a blend of ProMix and compost/bark stuff my local nursery suggested. The leaf attrition rate has ceased. Also the temps in St. Louis have also calmed down lately. Its no longer hot as the surface of the sun and only just hot as hell.