From Gary Pilarchik:
When planting potatoes in a container you only fill half the container with soil. As the potato stalks grow you can back fill the container and raise the soil level. Potatoes will grow out of the stem. This is a way to get more potatoes in your container. It is simple and easy to do. You can use soil or any brown material like leaves or dried hay. Just don't use green material like fresh grass clippings.
From: Jeff Bernhard: Grow Potatoes in your back yard! - YouTube http://buff.ly/1pWZEsl -- "In this quick video, I will show you how I have a constant source of fresh potatoes growing at any time through the year. It is simple and there is nothing like a fresh potato. In addition, growing potatoes are a great way for your kids to grow them, hill them and finally dig them out of the dirt. Fun for the whole family. Enjoy the video."