I had and still have potatoes growing in pots. I did plant a few in the ground and although the plant got huge the harvest wasn't as good as in my pots. Also it was hard to find the potatoes in the ground. I have heavy clay soil.
I have various sizes of pots because I kept finding new volunteers in my compost pile and used whatever I had left to plant them.
My best harvest came from a small, maybe 5 gal pot with two plants in it.
Just like kissal and Applestar said, you plant the, for me, sprouted potato skins near the botton of the pot. I used mostly compost. Hey, they were happily growing there when I found them.
Then as they grow you add more compost and soil. I watered them almost every day-after- they got large.
This is my most recent harvest and what it looked like in the pot. I have a few other pics I haven't put on my site yet.
[img]https://i600.photobucket.com/albums/tt87/Dianesgarden/PA011109.jpg[/img]
[img]https://i600.photobucket.com/albums/tt87/Dianesgarden/PA011111.jpg[/img]
[img]https://i600.photobucket.com/albums/tt87/Dianesgarden/IMG00063.jpg[/img]