Zone 4 can start planting peas,lettuce,radishes,and other cold temp vegs now. Typically, the last frost date is May 15 which is when you can plant tomatoes,pepper plants but they still should have a temp. cover on cool nights.Also plant cuc seeds,carrots,etc May 15. The soil is only about 42 degrees down 4"!(of course the seeds aren't planted that deep but plants can be)
Zone 3 is about 10 days later.
Peggy

Thanks so much - so much to learn.