Spring in the vegetable or flower garden is a carefully orchestrated series of events. The goal is to keep things moving forward with the warming season, taking into account weather predictions and, because those are just predictions, average spring warming trends where you garden.
Many gardeners use Memorial Day as a turning point in their gardening calendar. But Memorial Day weather in San Diego is very different from Memorial Day weather in Concord, New Hampshire.
A TURNING POINT
A better measure is "the average date of the last killing frost in spring" where you live. Note that this is just what it says, an average. In any year, that date might be earlier or later.
You can figure out that average date of the last killing frost online at a variety of sites where you just type in your ZIP code.