Not one to go by the good advice of others when I can just blindly improvise and see what happens, I made several quarts of kraut today and added a crushed up bag of frozen kale to the mix.
Mostly for the extra nutrition, since I don't really like the taste of kale.
I did bother to look it up on the web and saw that someone mentioned blanching kale before fermenting with some backslop, so I figured frozen and crushed would do just as well.
I'll respond to myself when I see how it's doing.