Wherever you are located, plant after last chance of frost in the spring.
Recommend you do not plant the whole potato. Sweet potatoes are normally grown from 'slips'.
Yield depends on soil and moisture conditions and care given to 'em.
Recommend you contact your local County AgriLife Extension Agent and Master Gardener organization - and peruse the following sites for info:http://www.diynetwork.com/diy/gr_fruits ... 47,00.htmlhttp://www.clemson.edu/extension/hgic/p ... c1322.htmlhttp://urbanext.illinois.edu/veggies/sweetpotato1.htmlhttp://www.ctahr.hawaii.edu/fb/sweetpo2 ... m#Plantinghttp://www.hort.purdue.edu/ext/HO-136.pdf