How was the South good for farming?
I am overstepping it here but I try to give an answer...
From what I read the South before the Civil War was traditionally dedicated to farming in particular using huge extensions to plant Cotton and Tobacco. Cotton, in particular, was very profitable being sold to England and to her textile industry.
[ Right before the Civil War, in 1858, Senator James Henry Hammond of South Carolina declared that Cotton is King. Those fields of white, he said, had the economic power to bring the whole world to the feet of the South. No one would dare make war on old king cotton. ]
The interesting thing is that these types of plants are well suited for warm/hot climates and I do not think are particularly suited for cooler environments (such as in the North).
I suspect that the climatic factors played a big role, steering the economic structure of the South towards farming as an almost exclusive choice/possibility.
Also, it is worth to remember that these types of cultivations needed big extensions of land and so big crops to be profitable. This implied the need of cheap manpower (no machines at the time) to harvest and cultivate.