We didn't try to grow any sweet potato's, but regular potatoes didn't do real good here this year. They vined and grew really well above ground, just didn't have any potato's much worth mentioning when we started digging them up.
Hope yours' do much better.
As for grapes, my Moms next door neighbor has them growing along the entire length of fence in their back yard.
They were there from the previous owner of the lot next door and to my knowledge, Jim (the new owner) hasn't picked the first one in the 10 or 12 years he's lived there.