Answer: This really depends on what you are planting. Some plants germinate best when planted very early at a cool soil temperature (peas or spinach for example) while some do fine in midspring (many flowers) and a few need warm soil and should not be planted until a week or two after your last frost (tomatoes, melons, moonflower vine). Check your seed packets for an indication.
Also, you can check with your local county extension (or a neighbor who is an experienced gardener) to try to get an idea.
Usually the average frost date works as a guide. The average frost dates may or may not apply this year, it has been a very odd spring. However you can check your frost dates at the following government web site.
I hope this helps you get a general idea of planting times.
Q&A Library Searching Tips