Here in New Mexico we have wild mustard plants growing well all winter. In the spring, they really take off and produce a lot of foliage and flowers - all without any supplemental water. They just grow in lots of untended (as well as tended) areas.
These plants have a very sharp taste. You can’t really use more than a leaf or two in a big salad. They retain the sharp mustard taste even when cooked.
However, I’ve just discovered that when I let them soak in a large pot of salted water for several days, they became pickled and lost virtually all of their sharpness. They are reminiscent of kim chi.
I don’t know yet if the pickling alone will do the trick or if they need to be in lots of water or maybe multiple changes of water. I had read that the mustardy substance is water soluble, so I put them in much more water than I would for normal pickling.
These plants are so abundant at a time when little else is growing that they could be a significant food source. And they grow wild everywhere here!
I don’t consider them invasive. They die back by the time the growing season is under way and they only start growing again later in the fall.