They will love your seeds, and think that you buried them there just for their digging pleasure... kind of like a treasure hunt... and OH, the dust bathing pleasure offered by that nice loose soil!! Seriously, you'll have to keep a fence between the chickens and your garden at all times... at least until it is very well established. Even then, your girls will eat any thing that looks tasty to them, and they will scratch exactly where you don't want them to!