http://www.thegardenhelper.com/potato.html
I definitely threw stuff at the bottom of the hole, a couple of shovelfuls of composted manure and a handful of Osmocote 14-14-14 for 4 seed potatoes.
My potato plants have gotten pretty big and already put out blossoms. I can probably harvest at the end of April. This picture is from a couple of weeks ago. The plants are even bigger now.