Answer: Shimpaku juniper is usually listed as a cultivar of Juniperus chinensis sargentii 'Shimpaku', but some list it as J. x media 'Shimpaku'. Proper name aside, Shimpaku juniper is a cultivated strain and it is likely that different forms of the plant are called Shimpaku in different areas as you suggest.
Our advice is to collect as many different strains as you can, from Japan, Taiwan, and elsewhere. Try growing some from seed. Interview the sources of these plants asking about their understanding of its growth habits and keep these notes. Grow these many different varieties and watch for the one that best suits your needs in Chicago. Such a process will take longer, but is the only way you'll know you have the best one.
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