Potato question
 

I have a very spreading potato plant area. It just began blooming
(little purple flowers with yellow centers.... Deadly Nightshade! Is
that related to the potato?)
My other question is, as this spreads and spreads, the center area is
a nest of bare stems. Shouldn't this be covered so that more potatos
form along these stems? What should it be covered with: soil, mulch,
grass clippings, or what?
Thanks.
Kira