These are more like garnet roots! I can see why sweet potatoes grow better down south. They, or at least this one, needed more heat, more sun, and a longer growing season than I could give it here on my shady porch in Pennsylvania. Although it did produce some lush growth and even flowered.
I wasn't sure when to harvest but I noticed that the soil was full of roots. The plant (from one potato!) had become root bound and it was needing water every day. Interestingly, when I found a "potato" it was often lodged against the side or growing along a root that had wedged itself into a crack. If the potatoes really took off I'd bet they could get into structure and damage it, like ivy on a building.