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.
