Ceresone, Here in z6b in eastern Ok, my grandfather always said St Pat's day was the time to plant potatoes. Onions go in the same time. I start broccoli and tomatoes the first of March on the hot bench on the glassed porch, and plant both in the garden the last average frost date, April 15. Could start tomatoes earlier and think I will start a few earlier this year, but my plant bench is pretty full of sugar snap peas starting Feb 15 and going in the garden Mar 1.

I'm always afraid to depend on a frost date, myself. I think thats about our last offical date too, but I can depend on a frost about May 10. When I wait--it dosent frost--if I plant early, it will frost.
I'm trying to decide if I want to take a gamble, and start my plants. Then, too, I have onions coming...

St. Pat's day was traditional in Christian Co., Mo. where my grandparents lived, but grandma always just planted her garden all but tomatoes and peppers on Election Day in April.
I think April is plenty early. The potatoes will come back from a pretty hard frost and still produce.