Nice! Have you checked the roots to see how they are doing? With that kind of growth you should be able to see, or feel potatoes.

My jaw hit the floor. I can not do that in Michigan. I wish you luck with the tubers.

Ed,
I only checked the first plant - not much that I could find but I didn't dig around too much.
Glib,
I'm sure you could with a tunnel, or at least some row covers. Our July has averaged a chilly 63 degrees with several nights in the 40s and even a couple in the 30s. I'm actually surprised the sweet potatoes shrugged all that off. The tunnel runs about 10 degrees warmer than ambient at night (2 layers of row cover plus a layer of poly on the outside, and plastic mulch on the ground to keep the roots warm).

Yeah, they do take a long time, but when they hit, they hit. If you can do that in Z2, you could do anything. How about melons? Did you use skinny pvc pipe to make the hoophouse?

Very impressive. I hope it turns out to be worth the effort, but, if later it looks like tuber production will be slight, don't forget that the foliage is a very nutritious cooked green. Goes really well with cooked tomatoes.

Ed,
Yes, I used PVC. The structure looks like it's about to fall apart, but it has been looking like that for two years now. However we are moving this fall and I'll have to tear it down. I thought about melons but they take up so much space for the yield.

pnbrown,
Thanks. I was reading up on sweet potatoes and read that long days favor vegetative growth. That doesn't portend well for my crop since we get frost while the days are still longer than nights. If that turns out to be true, it could be a major impediment to growing them here.

You've got a at least a couple different varieties, looks like.

FWIW, if you try them again another season, the Korean Purple (purple skin, white flesh - yellowish when cooked) has proved to be by far the best producer here, along with of course the reliable ole Beureguard. However I much prefer a white-fleshed SP over the latter.