I've never heard of Crepe Myrtle growing as far north as N.J. which I think contains hardiness zones of 5 to 7 (zone 7 being along the coast) and they might have issues with extended cold winter temperatures in the north or central part of the state.
This page shows Crepe Myrtle being hardy from zones 7 - 9:
http://landscapedesignbylee.bl... but I decided to google "Crepe Myrtle for N.J. gardens" and a couple of Southern N.J. nurseries popped up that sell them:
http://www.circlegardencenter....
http://damblys.com/
You could always get the more dwarf varieties and keep them containerized.
