I got the idea from this article in the Seattle Times. The hook is that you can grow a lot of potatoes in a tiny space; just what I need.
Greg Lutovsky, who has been growing potatoes as a business since 1993, says you can grow 100 pounds of potatoes in 4 square feet. All it takes is some lumber, seed potatoes and careful attention to watering.The story was enough to get me started, but it's a little short on practical advice. For that I turned to Sinfonian, who meticulously documented his potato-in-a-box efforts last year.
The idea is to pile up soil around the growing potato vine, adding more soil--and boards to the side of the box--as the vines get taller. Potatoes will grow between the seed piece and the above ground plant.
When the plants start flowering, after about 100 days, you can remove a board or two from the bottom and fish out a couple of potatoes. Or you can wait until frost kills the plant in the fall and harvest them all at once. There are plenty of sites that explain how to store potatoes. With a bit of luck, I'll be doing that this fall.
If you want to grow vertically, there are several alternatives to choose from: grow bags, wire cages, stacked tires, large containers. All had drawbacks, so I chose to make my 3'x3' bin out of cedar fencing boards and southern yellow pine. I gave all the pieces a coat of linseed oil, hoping that this will protect the wood from rotting.
I bought, and then chitted, 3 pounds of Inca Gold seed potatoes from Ronniger Potato Farm. Inca Gold are late season potatoes, an important detail for this type of growing. According to Sinfonian, early season varieties only set fruit once, making them bad candidates for potato towers. You'll end up with a few at the bottom of the box and that's it.
I just planted my seed potatoes today. As they grow, I'll add more cedar boards to the sides of my box and cover them with dirt.
I'm following the same method of piling up soil around a growing vine--but with sunchokes-- in SIPs on my roof. I think you could do the same with potatoes.
[8.26.09, update on potato box]