Growing potatoes in a bag is not something I have ever tried, but my friend, Jan, in New Orleans, LA took photos of her potatoes planted in a bag. She places soil in the bottom first, then as the green plant grows she covers it with more straw. When the potatoes are ready, she just splits the bag and there are the potatoes, no digging! She is going to try kitchen bags next year because these bags were too large for her plants and needed huge holes for drainage.
Are you adventurous enough to try this?