Q.Is Zoysia grass used in shaded areas
I have not had very good luck with Zoysia grass growing in Oklahoma. Is there a reason why this grass has not been a good choice for Oklahoma? I have planted in the shade and in the sun and both places get choked out by other grasses.

Certified GKH Gardening Expert
It is considered a warm weather grass, and you would want a cool weather grass. Zoysia goes dormant in cool weather, which then gives weeds and other grasses an opportunity to establish within the zoysia.
This article may help you with selecting a cool weather grass that will tolerate shade:
http://www.sustland.umn.edu/maint/coolseas.htm