Is my Citrus Sugar still good?
I've never made Citrus Sugar, but I certainly have made vanilla sugar.  Crystaline sugar soaks up the moisture, so if bacteria or mold were to invade the pot, it would be dehydrated quickly and wouldn't survive, let alone thrive.  They need a good bit of moisture to reproduce.  I've never had a problem with my vanilla sugar and it doesn't take long for the vanilla beans to turn into little vanilla toothpicks.