Find a Wild Potato in the grasslands and use a Sharp Stone or shovel to harvest Wild Potato Tubers. Plant the tubers in a Deep Tilled Row then water (with Bowl of Water or Full Water Pouch). After 2 minutes you will get Potato Plants, to which a Bowl of Soil must be added. After 4 minutes, it will mature, and 5 Raw Potatoes can be harvested using a shovel. Harvesting all potatoes will create a Hardened Row.
Place a raw potato in a Bowl of Water. After 30 seconds it will turn into Sprouting Potato which can be removed and cut with a Flint Chip or knife. The split potato sprouts can be planted into a deep tilled row to begin the cycle again.