March 15 is when many start their seeds. They can be put outside 15 May, although last year it was still dicey 15 June and then we had frost the first of August. Hope you can put your seedlings out this year.
We purchased one of those COSTCO portable greenhouses sevral years ago, so we go from the house to the greenhouse to an open greenhouse then to the garden.
Maybe spuds will work in the raised garden beds this year.