Succession planting seems so esoteric, so advanced (to this newbie veg gardener) that I've been intimidated by the very notion of sowing vegetable seed throughout the season. So I'm exploring the best sources I can find on the subject and passing them along.
If you've never visited the blog A Way to Garden, I recommend you check out this top-ranked individual garden blog. Its popularity is no surprise because blogger Margaret Roach was Martha's Stewart Living's editorial director for decades and having retired from the fast lane, she's put her many skills to use online, free for the reading.
So when I heard Margaret mention on her weekly radio show that she'd finally devoted the time needed to explain succession gardening, I immediately looked for it online and liked what I saw. If you prefer learning by listening, she explained the basics during her 6/7 radio show. (Don't be shocked to hear mention me at 20:16 minutes; we had a good-natured disagreement over the identification of a creeping sedum. She definitely won that round.)
Margaret's in Zone 4, so adjust the dates by two weeks or so, and consult the Planting Dates for Maryland from our (most excellent) Extension Service. Or choose from dozens of excellent online publications about all types of gardening.
About the photo: Robin Ripley's vegetable garden is in Calvert County. She blogs at BumblebeeBlog.com.