Green’s Dictionary of Slang

magnolia curtain n.

[SE magnolia, generic synon. for the South + play on Iron Curtain]

(US black) the Mason-Dixon (40°N) line that divides the American north and south.

Soundings mag. 308: The Southern Temper is a balanced, workmanlike job of reporting and analysis, and it deserves to be read widely, both above and below the Magnolia Curtain.
[US]D. Booth Atlantic Monthly Aug. [article title] Behind the Magnolia Curtain: A Yankee in Mississippi.
[US]Tay Falco [song title] Behind the Magnolia Curtain.
[US]D. Buring [dissertation title] Building gay community behind the magnolia curtain: Memphis from the 1940s through the 1980s.
Alabama Shakespeare Festival [Internet] Homemade Love – A woman. A man. A marriage and a secret. The Magnolia Curtain is upturned…and a southern family will never be the same.