I live in ne MD and I start my tomato and pepper plants in the first week in March. Once they have some size I transfer them to a mini-greenhouse. We can have frost up to mid May. I also have those "Walls of Water" and I set out a few tomato plants using those. If it's going to be below freezing I store the plants in the garage.
Last Winter was very mild and I plowed the garden in Feb. You need to figure when you have your last frost in your area. My wife and daughter both have Earth Boxes and they planted
last year in March. They're on wheels and can be rolled under cover. She had tomatoes before I did. Hal