I've grown flowering maples numerous times, typically as a summer annual as most are not winter hardy. Have even overwintered a few as a houseplant. They really do not require any more attention or care than most other annuals or seasonal plants. Personally, I would opt for more of a 5-1-1 mix rather than the gritty........abutilons seem to appreciate a consistently moist soil that is easier to monitor in the 5-1-1.