As you add dirt to the base of the plant, the main plant sends out new roots from the main stem which then produces more potatoes. You have tol have enough plant leaves left above to produce the necessary nutrients for the plant to continue to grow.

They use this principle in stacking tires for use as planters for potatoe farming and getting the most out of limited plants.

As the plant gets bigger, another tire is added with more dirt and so on,,,,,lots of potatoes at the end when harvested.



As a side note, Tomatoe plants will also add roots along the main stem if dirt is added. Some varieties are sold with instructions to do the initial planting with two thrirds of the plant into the dirt.