It would probably prefer an ericaceous compost. I potted one on a few years back and I've got a vague feeling (sorry - not very helpful) that I added a bit of grit and probably didn't add extra fertiliser. I also prefer to use soil based composts (john innes style) for containers as I find they don't blow over so much and don't get so dry so fast.
Is it a japanese mapel? Lots of them are gorgeous - I hope it does well for you