Every year I offer vegetable plants, and every year it tends to vary although I do have my favorites as do most of you. Space is usually at a premium (I need another greenhouse, but I suppose I'd fill that one too!) and I don't want to plant too soon so I wait until the weather is more friendly. For things like cucumbers, squash, and melons if I plant them too soon, they will eventually languish in their pots waiting for transplanting. Not good for you, not good for them. Our average frost date is May 15th but we've had one as late as June 1st.
Some veggies (squash, cucumbers) don't like their roots disturbed so overgrown plants don't gain you any advantage over direct seeding. I try to time it so that most things are ready for the last week of April and the first week of May. Check back to this page from time to time and refresh your screen. News things will be popping up all the time.
Vegetables
Cool Season Vegetables
Summer and Winter Squash (coming soon)
Cucumbers (coming soon)
Warm Season Vegetables