To grow potatoes as far north as you are, where the ground is so much cooler, a container may be your best bet. The soil will stay warmer and you can extend the season a bit if you have a shed or garage to put it in at night when it starts to cool off. Z4 warm season isn't long enough to get a crop of sweet potatoes from in the ground.

I get a rash from the latex sap, so there's no way I'm going to try to eat any of the foliage or stems.

Three are in a raised bed, and three are in a really big BLACK container. I will try putting black plastic on the ones in the raised bed. This garden is south facing. It gets sun from 8:00-7:00. We are supposed to have above normal temps this summer. I am confident of a big harvest. I will update. Remind me if I forget.

Sounds like you're doing what you can do! Best luck & good vibes!