I am under the impression that people grow potatoes in bags, containers, stacked up tires and so on because they get higher potato yields this way. The way I've heard it explained is that you plant the seed potatoes on the bottom and wait for the plant to grow. Keep adding soil every few weeks until you reach the edge of the container. Supposedly the roots will keep growing upward as well, and the whole container will be filled with potatoes.
I tried growing this way this year, and all my potatoes plants initially grew like crazy. I added soil as the plants grew, and eventually, I reached the edge of the container. The plants grew a bit more but mostly stopped adding new growth. Fast forward and my plants are starting to die back, so I harvest potatoes. To my surprise, all the potatoes were in one layer in the bottom of the container where I started the seed potatoes.
Reflecting back it seems pointless for the potato to put all that energy into growing a long stem and tons of leaves if I am just going to cover them with soil. The container did make it easier to harvest, but I did not have potatoes growing upwards in the soil as I expected. Is this an unusual result? Why bother growing in containers at all? Does anyone have any evidence that potatoes will grow all the way to the surface of the container?