The day I found them, it was still way too cold for planting them out, so we decided to try a variety of things to keep them from using up all their energy and petering out before getting in the ground. For most of them, we broke off the long tendrils, leaving little stubs, and put them in a plastic bag in the fridge, hoping to slow them down again until we could plant them outside. The tendrils we put in a jar to see what they would do. The four other little spuds you see below, we planted in a pot.
At last, it was time to harvest! We thoroughly dug through the patch where we'd planted the shoots and the refrigerated taters, and found only a few stunted tubers. Strangely, some of them looked exactly like rough-textured rocks, and we could only tell they were potatoes when we broke them and the interior was brilliant purple! A week or two later, we harvested the potatoes we had transplanted from the pot, and had more success. For some reason, this variety of potato has a tendency to form a small potato attached to the end of a larger one, resulting in several that looked like little people (or babies, or mummies). Below is the entire (rather scanty) harvest: