As the seed potatoes sprouted and sent up vines, I added a new board to each side and covered almost all the new growth with fertilized potting mix. In a couple months the vines were all the way to the top. The idea, cribbed from an article in the Seattle Times, was that tubers would sprout along the entire length of each (covered) vine to fill up the entire box with up to 100 pounds (!) of new potatoes.
Ordinarily potatoes are planted in the ground and produce tubers at the ends of the roots. Here's what a potato plant looks like in normal growing conditions:By continually covering the growing vine with soil, I'm turning the green vine into a very long tap root. Off of the entire length of that root, the plant will produce tubers.
If you're looking for instructions on growing potatoes in smaller containers, Love Apple Farm has a good tutorial.
They started setting up flowers around the 1st of August. Since these first blooms I haven't seen many more. That doesn't seem right.
Two weeks later, it's time to check for new potatoes, at least according to this link.
"You may begin to harvest your potatoes 2 to 3-weeks after the plants have finished flowering. At this time you will only find small "baby" potatoes if you were to dig up a plant. Potatoes can be harvested any time after this, by gently loosening the soil, reaching under the plant, and removing the largest tubers, leaving the smaller ones to continue growing. If you want late potatoes for storage, wait 2-3 weeks after the foliage dies back."
They said baby potatoes, nothing about peanuts.
After I took off the bottom board on one side, I stuck my hand in about 5" looking for potatoes. All I found was a peanut, probably left by a squirrel when there wasn't much dirt in the box.
I'm going to let them grow a little more and then pull the whole thing apart in mid September in search of my 100 pounds of potatoes.
[Update 10.6.09, Potato Harvest results]