The sweet potato tubers are placed on a layer of potting soil and then covered just barely with soil & a thin layer of vermiculite to hold extra moisture. As they sprout and make slips, the Martins add a thicker layer of potting soil to encourage the slips to grow more roots.
I picked over one thousand slips with Mrs. Martin while her husband and son were planting watermelons in the field using their team of percheron horses to pull the wagon carrying transplants.
We made mini-hills in our garden before planting because these taters prefer a warm soil that drains well. Planting accomplished before lunch time as the thunderclouds filled the sky holding the first drink of rain for these new transplants.