Answer: Crepe Myrtles are marginally cold hardy in Chicago. Only the more cold hardy varieties have a good chance of survival here. The National Arboretum has been doing some breeding work with Crepe Myrtles to increase their cold hardiness. The following varieties are good ones for cold hardiness, but none is a mini-dwarf. 'Pecos' is a deep, neon rose-pink and 'Zuni' is a bright purple with a tinge of pink. ('Acoma' Crepe Myrtles are also more cold hardy.) I've have two ?Zuni' in my yard for three winters now and they come back each year.
I consider them small shrubs or even a large ground cover. I cut mine back early every spring down to within 4" of the ground and the plants resprout from the base. They grow back quickly (mine right now are probably 18" tall) and will bloom spectacularly later on this summer.
It's disappointing to me that they won't get taller because I think that the bark of the trunk of these plants is one of their nicest attributes, but they usually won't winter here and die back to the ground unless they're placed in a very protected place.
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