Last weekend I worked around these brassicas to lasagna garden the rest of the patch. My first try at this low-labour, organic and failsafe way to fertilize the garden over the winter, and keep weeds down at the same time. The part that isn't easy is getting enough stuff for the layers. The idea is that you layer browns (newpaper, leaves, etc) with greens (unfinished compost, grass clippings) to make a 2-foot high lasagne of good stuff to compost. Over the winter the stuff will "cook" and sink down, much like your backyard compost bin does. You can plant directly into it in the spring and don't need to dig or turn the soil first.
I've been saving leaves, newspaper, and bought a bale of hay for the undertaking. Still I was hard pressed to get four layers at 6 inches to a foot thick. Here are the different stages, working around those brassicas I'm not giving up on, and a few beets and carrots still in the ground.
Garden bed ready with old plants pulled out and set aside to be thrown back on in layer 2