Sweet potatoes in Minnesota
http://www.motherearthnews.com/organic-gardening/growing-sweet-potatoes-zm0z11zsto.aspx#axzz2PXf78Np0. I prefer to cite extension references however success with sweet potatoes is more than just planting them and this article is comprehensive and covers all the specifics. Good luck they are fun to grow and the vines are prolific and lovely. Remember too that the ornamentals were not bred for taste.