Hello,
I think you will be fine with Sweet potatoes, I planted mine late April the last 2 years and had good harvests, they do like warmth, so it is hard to plant much earlier here.

good luck

I planted sweet potatoes in June last year and got heaps!

With record rainfall last year (I received 81 inches), it isn't surprising that your grap*s were sour. Fruit needs a dry environm*nt during last stages of development, to concentrate sugars for sweetness. Water will make the fruit larger & more plump, but at the expense of flavor and sweetness.
I assume you are growing a table-grade (edible) variety.

There are several varieties of swe-et potato available, with maturity from 90-120 days. Even with the longest maturity type, you have at least 150 days before first frost and probably another 30 days beyond that.
Do you have an organic garden? There are 2 or 3 varieties that are insect, disease & nematode resistant that organic gardeners use.
Lesson learned during my youth; From about age 7, until adulthood, my family farmed. Everything we grew, vegetabl*s (h*me gard*n & commercial), fruits, grains (wheat, soybeans, corn) and all other crops were grown organically. It was the most economical way to produce any crop. Today that label costs extra!

Thank you all.

@roswell_organic: I agree. Thats what I thought.
@GGG: All the way in June! Wow. Mine soil needs more prep; I planted them really close; not sure how the tubers will do.
@Georgia_rose: Organic baby....all the way organic. I grew table grapes (green and red ones; forget their technical names). I wasn't sure if I picked it too early? I am big zero in growing things and have no grape experience. I have no idea how to prune...new shoots...old shoots...I had them on a $20 trellis...then the vines grew massive in one year and Iron trellis was bending...so I transplanted them in Jan/Feb. They needed pruning but i don't know what and how to do it. I put two posts in concrete and put 10 gauge wire. The two transplanted vines are sprouting. The one one that I didn't transplant are already having baby grapes and lots of them. The sweet potatoes were from lowes I think. I tried to grow it in a glass with tooth picks...no luck. It rotted. :(