Question
When should I plant Zoysia Grass plugs in North Central Georgia?

Answer
When your Soil -- NOT your AIR -- warms up consistently to 75 degrees F, it's time to plant a Warm Season Grass.  

Watch for Soil that hits 75 to 85 degrees F every day.  Zoysia roots revel in those temps.  You can check your own plot at University of Georgia's online 'Weathernet' Soil Temperature Calculator:

http://www.georgiaweather.net

Artistic Gardens & Landscape Design, a landscape design and installation firm in Texas, picks Zoysia sprigs instead of plugs for its customers.  DIYers can cover small plot areas with plastic to retain heat and spur establishment:

'Sprigging is the least expensive method of planting Zoysia and usually gives a faster rate of cover than plugging.  Keeping the Soil moist during the establishment period of most critical with sprigs.  Small plantings can be covered with a clear polyethylene tarp to maintain adequate moisture and increase Soil temperature in the early Spring.  The cover can be left in place for several weeks.'

They post their full essay on Zoysia at their website:

http://www.artistic-gardens.com/Zoysiagrasses_-_An_Emerging_Texas_Lawn.pdf

Soil pH should float between 6.0 and 6.5 for best results.  You can read more details for successful Zoysia plantings at the Seedland.com website:

http://www.zoysias.com/preparation/index.html