Well, several months ago I noticed that the potatoes in the pantry were going bad, so rather than toss them in the garbage, I wanted to see if these things would actually grow!  I never thought it would work, so I just dug a hole in the backyard, and threw the potatoes in about 1ft deep. Covered the hole with dirt and quickly forgot about it.

Fast forward to spring, and I noticed along with all the other weeds in the backyard, we had some "different" looking plants... right where I buried those potatoes. Just in case these were the tubers we cordoned off the area so they would not get trampled, and started to water the young plants (which we hadn't done before). I figured I would be stupid if these were really just weeds that we were caring for, but fast forward now to early summer, and lo and behold! - a flower has blossomed!

I quickly googled it, and confirmed, these babies are actually the long-forgotten potatoes! These have to be some hardy plants to grow in the rocky dirt in our backyard, but here is the pic:

http://img510.imageshack.us/img510/784/dscf0043g.jpg

and for comparison, potato flowers via wikipedia:

http://img8.imageshack.us/img8/8030/potatoflowers.jpg

Now all I need to know, is when to dig some of these up

I wait until the tops die off.  

You might be able to dig them up sooner.

That's all we did this year, all the potatoes we had left from last years crop that had grown roots we just cut em and planted them with the eyes/roots sticking up. They started growing like crazy in no time. We dug ours up at the very end of fall like October. We had 70lbs of taters it lasted us October- March/April!