About a week before planting, place seed potatoes in a warm spot. When the sprouts that form are about 1/4" to 1/2" long, the potatoes are almost ready to plant. Cut large seed potatoes into chunks about 2" wide. Each piece should have at least two sprouts. After cutting the seed potatoes, let them sit at room temperature for two or three days.
Use a pair of scissors to cut several drainage holes in the bottom of a 30-gallon black plastic trash bag. Roll down the sides of the bag and fill about one-third of the way up with potting soil. Place the bag in an area of the garden that receives full sun.
When the potato plants get about 6" to 8" tall, it is time to add more soil and straw to the bag. Add enough soil so that just the top few leaves poke through the dirt. As the potato plants grow, continue to unroll the bag and add more soil. Keep the potatoes well watered but not soggy.
One clue that the potatoes are almost ready to harvest is that the leaves will yellow and the foliage will die back. At this point stop watering and leave the potatoes alone for two or three weeks so that their skins toughen up. To harvest, slit open the side of the bag to release the potatoes.