Question: Use old potatoes to make more.
Option 0: Get a large pot and fill 1/3 of the way with dirt. Plant your old potatoes and then fill with the rest of the dirt. Water carefully and watch grow.
Option 1: Get a large pot and fill 1/3 of the way with rocks and dirt. Plant your old potatoes and then fill with more rocks and the rest of the dirt. Water carefully and watch grow. The rocks help provide nutrients.
Answer: 0