I don't remember that my grandmother dusted her potatoes with anything.
I do remember that she left them outside in the shade to dry for about a week before adding them to a bed of straw in the root cellar. She also brushed them off with a short handled broom to get the dirt off; she wouldn't wash them because she said to get them damp would cause mold.
Then she put them in straw, added more straw and then covered them with an old burlap feed sack.
They lasted all winter long that way, bedded in the straw; but I really don't remember dusting them with anything, just brushing the biggest part of the soil off.
Good for you for growing those potatoes!!
