Fold the sides of a 50lb horse feed bag down, fill with dirt and add seed potatoes is literally all I did. We go through lots of bags, so I have many empty ones. I have a problem with weeds (thistles) and oregano taking over everything in the garden area, so this was my lazy man's way of avoiding weeding.
I also have a giant compost pile consisting of mostly wood shavings and horse manure that I planted about a dozen potatoes into as an experiment, along with a couple dozen carrots. So far they seem to be doing really well.