When selecting, choose those that are firm and plump, avoiding those that have shriveled skins, sprouting eyes, soft spots, blemishes and green spots. Store potatoes in a cool dry place. They will keep at room temperature for up to two weeks and longer when stored in cool temperatures. Do not store in the refrigerator because the cold temperatures will convert the starches into sugar and the potato will become sweet and turn a dark color when cooked. Do not store with onions, the gas given off by onions accelerate the decay of potatoes.