I started blanching and freezing my abundance of greens last week. That left me with the long stems of kale, collards, broccoli, and beets. After I had a big bag of them in the fridge, I chopped them all up and put them in the crockpot. I added extra cabbage leaves, plus one onion and a couple bay leaves, stewed them together in a pot for a day to make a lovely organic vegetable broth.
In case you are wondering what I did with that broth. I removed all the now mushy vegetable matter, leaving the liquid in the crock pot, added white beans, green chiles (from last years garden), 5 chicken thighs, and hot sauce to make chile. The kids love "bean soup" as they call all my chile variations.