We grow a ton of mustard greens in our winter garden, primarily for grinding and mixing in with the dog food (we feed raw, and add in some greens, otherwise the dogs start munching on the garden). Usually they start to bolt, we get one more harvest, and then we pull them.
This year we let them go to seed, and it was pretty amazing. All of these flowers -- which are quite edible and spicy! -- grow and then turn into these seed pods. I'm not sure why it never occurred to me, but mustard seed comes from mustard greens. It was an enlightening moment, but also an embarrassing one. Seriously, how did I miss this?
Anyway, I pulled some of the plants and let them try, then cut the stalks, shoved them in a pillow case, and beat it around to break up the pods.
http://dl.dropbox.com/u/27335/mustard.jpg
Mustard seed! I stuck them in the dehydrator for a few hours.
Not all have that spicy mustard flavor, so I may have pulled them out of the ground before the seeds were mature enough. We had more that I left in longer and the pods were much bigger, so we'll see how they turn out at the end of the week when they should be dried.
An interesting fact about mustard greens? They're a self perpetuating crop. If you can dedicate an area of land to them, they'll seed themselves and regrow every year.