Farmette, I think it is cool that you are growing Sweet Potatoes in Wisconsin. My little bit of knowledge about sweet potatoes grown locally is in East Texas. This link is pretty good
http://traveltips.usatoday.com/golde...as-106632.html
I personally, would let out extra water, but I don't grow sweet potatoes anymore. In November and December they will sell for 20 cents per pound here.
I wish I could help more. The link above is the area where my step Mother of 36 years grew up - she loved that area more than life and everyone else.