It would depend upon the planting calendar you are referring to, but in most cases they indicate if you are planting 'transplants' or seeds. So assume seeds unless noted elsewhere. Sometimes it says, "Start plants indoors this long before planting date". So that is when you would start seeds OR just go buy plants on the day indicated to plant in the ground.
Unfortunately the link to the excellent resource, Extension's Growing Your Own Vegetables is broken. But here is another way to access it: https://catalog.extension.oregonstate.edu/em9027