I attended a workshop recently through Trade School that taught me how to make suerkraut from ornamental kale. You've probablly seen ornamental kale; it's used in winter landscaping. It looks like this:
You can pick it, cook and can it; or pickle it like you would cabbage. Or eat it fresh. Sadly, the kale in my neighborhood is all limp, floppy, and brown. If you can find some crisp kale in your 'hood, harvest it and stow it away for the challenge!
Below are some tips and a recipe from my teacher, EmCee CM:
Technique: collect leaves before they brown or wilt, larger, outer leaves first. If you collect from a variety of plantings you can fill your basket without disrespecting anyone’s display, and, more to the point, you can allow the plants to continue growing for future forays and for other foragers.
Ornamental Kale Sauerkraut
Wash your harvest in cold water (mix in vinegar or baking soda if you like for extra cleaning power). Chop kale fine and pack in a large jar, Tupperware container, or for a big batch, a five gallon food-grade plastic bucket works great. Layer the kale with plenty of salt and any other veggies and herbs you like.
Press firmly the whole business to the bottom of the jar and weigh it down with a smaller jar full of water (capped) inside the big jar. Or use any other press strategy you can think of for the container you’re working with (for a big bucket a dinner plate with a milkjug full of water as a weight works great). The goal is to keep the kraut submerged in its brine as it ferments. Over the next 24 hours, the salt and pressure will draw moisture out of the veggies, making a natural brine for the kraut to soak and ferment in.
Let it sit on the counter for a week checking regularly for taste and texture and mixing it around so it ferments evenly. It should remain somewhat crisp and crunchy and always submerged. Any bits that stray up above the brine level will dry out and could possibly form mold. Just discard them. During this week, leave the cap of the big jar loose so that air can escape.
When it tastes ready to you, refrigerate as you use it. It will keep for many months. Or you could can it in sterile jars and a boiling water bath for long-term shelf storage. Follow the instructions that come with the jars (Ball jars and Mason jars are available in some hardware stores and grocery stores and online). Eat it as a side dish, with hotdogs, as a soup ingredient, as a filling for crepes and savory pastries, etc!
p.s. A great resource for fermented foods is Sandor Ellix Katz’s book Wild Fermentation.