I want to grow some veggies in my backyard. I live in the mid-atlantic area. When is the best time to start planting and what are the plants most likely to thrive in this area?

Spring is he best time. but you need to check what "zone" you are in. You can start by planting seeds in the house and when the time is right re-plant them outside.

As the answers above state the major window of opportunity has past. But, you may still be able to plant a few cool weather types like peas, lettuce, spinach and radish. Another thing to plant this time of year are green manures and cover crops. RScott