March 1st to 10th is usually optimum. You can plant earlier but it is likely the plants will be nipped by frost which just slows them down.

Aside from potatoes, now is the correct time to plant english peas.

DarJones

My soil here in central northern Alabama is not quite warm enough yet for the earliest spring crops like peas, but it's close. Perhaps next week.

ACES says to plant Irish potatoes in July, but I've talked to many who plant a spring crop as well.

St. Patrick's day. Misterbaby.

Check out this link - it should help you: http://www.agardenpatch.com/Your-Zone-and-Average-Temperatures.html