This is my first year getting grapes. They are supposed to be an edible grape that I bought from a nursery a few years ago, the grapes are dark purple now, but they are small and very sour. Will they sweeten up if I let them stay on the vine? Will they get better next year? Do I need to do anything to help them?

For corn, this is the 2nd year I've grown it in the ground and they get about 3-5' and stop growing and form the tassels at the top. I have a few silks that formed, but not many. I'm not sure yet if any corn will form, I did try to hand pollinate them. I don't remember what variety I got, but I think it was American something, last year it was a different variety. I have them in 3 rows of about 20 each row. I gave them some 20 20 20 fertilizer a few weeks ago, is that the problem? I'm not sure what else it could be.

I'm in zone 5b.