Cool!
We did a bit of research about them and found several sites where people had tried it and had great success. [And we found one site at the University of Oregon where they said it was a myth and impossible to grow potatoes that way. Apparently they never even tried it. Okaaayy. I'd be peeved if I were an Oregon taxpayer.]
Eric built two towers, using 2x4s for the posts and 2x6 or 2x8 for the side panels - whatever he had laying around.
I put the towers over newspapers and lined them with more paper to keep the blasted grass and weeds out of the edges.
The idea is to start with one level of sides, plant your potatoes, then as the greens grow up, to keep adding dirt/fill so that no more than 4-6 inches of green shows.
The stems will keep producing potatoes as long as you cover them quickly while they're new. If they get too long, they won't make potatoes, even if you cover them up later.
When you get to the top, let the greens get as big as they want and keep it good and watered. I'm toying with the idea of putting some soaker hose of some kind in the middle. Not sure yet.
Since I took this photo last weekend, we have added two more levels of wood. I have to check the greens EVERY DAY because they are shooting out of the ground. You want to cover the stems as new as possible.
One of the sites we saw recommended using late variety potatoes for the tower, so that's what we used.
What will we fill with? See those straw bales between the towers? Those are what we used over the winter for the cold frame. They're kind of wet and old and clearly are growing fungus in places, but I wanted to see if that would work, so we're using them. I'll layer with sand, too for good drainage.
How do you harvest? Unscrew the wood from one side and empty it out. We've heard tell that you can undo the bottom and start harvesting from the bottom if you like, but you've got to put the soil back. We'll be harvesting from the top or near the top anyway.
So far this is really fun. We'll keep you posted.
UPDATE: 9/22/2013. After two years experimenting with these, we're abandoning this way of growing potatoes. Very poor harvest both years. With wood up the sides [2012], the potatoes are hard to keep uniformly moist. Potatoes did not form up the stem as they were supposed to. We only found them near the bottom. With chicken wire sides [2013], the plants had better access to sun and water, but we still had a poor harvest - tiny tiny potatoes. We're going back to regular raised beds.
