Boggy places are wet, muddy, and sloppy. If you plan to hike through that boggy wetland, you're going to have to wear your waterproof boots!
The adjective boggy means "like a bog," and a bog is a swampy wetland with a whole lot of moss. Marshes and swamps, while not bogs, can definitely be described as boggy. Your boggy yard isn't quite right for the vegetable garden you planted. Next year, you should try some cattails — they love that soggy dampness.