The map above is based on average dates when you can begin setting out plants without fear of frost in the U.S and Canada.
Many old garden hands in Mid-Atlantic states, for example, will tell you that the first day for outdoor spring planting is actually April 20, when they will set out frost-resistant varieties of vegetables (peas, radishes)
before planting warm weather crops and flowers nearer the end of the month.
In short, use the map as a guideline only, and if you are still unsure of the safe frost-free date in your area, take advantage of local garden wisdom by asking knowledgeable neighbors when they begin planting their spring gardens.
Climate is what we expect, weather is what we get. Mark Twain