Memorial Day?
It really depends on where you live, which climate zone and all that. To use Memorial Day as a 'safe-to-plant' date only works for some people.
There is a planting calendar on ATP where you can plug in your location and it'll tell you when to plant many types of veg. Look for 'Goodies' on the left side of the screen and find the planting calendar.
http://garden.org/apps/calenda...
Oh, for Memorial Day I usually go to the cemetery with the American Legion that day and then we have a big picnic meal at the hall afterward.