Store-bought potatoes may form eyes, small protrusion with green sprouts, if not used in a timely manner. Potatoes with eye sprouts may be planted in the garden and could produce a new crop of potatoes. Select organically grown potatoes to avoid genetically modified seed, as these are less likely to form new sprouts.
Potatoes grow well in hills or mounds. Mound the soil around the potato plants as they mature. Dig trenches 4 inches in depth the length of the area, leaving approximately 12 inches between each trench. Allow the displaced soil to mound along the side of the trenches. Alternatively dig small holes approximately 4 inches in depth in the selected area, leaving 6 inches between each hole. Mound the displaced soil around the hole. The prepared potatoes are placed in the holes or trenches and covered with the displaced soil.
Set potatoes with eyes in a box in indirect sunlight. Allow the eyes to continue sprouting. This is called chitting. The eyes should form small, slender stems 1 to 2 inches in length. Cut larger potatoes into sections, but leave small potatoes intact. Each piece of potato should have two sprouts with healthy stems. Place the cut sides upward and allow drying overnight. This is called scabbing and reduces the chances of rot forming on the newly planted potato.
Place the potatoes in the prepared trenches or holes. Place each potato or potato piece with the sprouted eyes facing upward. Downward facing eyes will fail to sprout and form a plant stem. Cover the planted potato with soil, leaving the top slightly mounded. The potato plant stem grows upward, but the roots, the actual potatoes, grow outward in the mound. Water the newly planted area with a light spray so as not to disturb the planted potatoes, but water deeply.
As the plant gains height, continue mounding soil around the plant so that the bottom third or more of the stem is covered. The potatoes will form within this mound. Add a mulch of straw with each new mounding. This provides the plants with nutrients, as well aiding in moisture retention. Avoid over watering the potato plants, as the newly forming potatoes are prone to rot. Water approximately once a week with a light spray until the mounds are moist but not wet. After the plants have flowered, carefully sift through the side of the mound to locate "new" potatoes. For larger, mature potatoes, harvest after the plant has died back.