Another "weed" that has earned a spot as a cultivated plant in my garden is lambsquarter. A bountiful source of nutrition for humans and animals, and it grows with little effort in my area (short season).
Lambsquarter is a close relative to quinoa and amaranth. For humans it can be eaten like spinach, with a similar texture and slightly milder flavor.
The plant grows about 30" tall and wide, but is not sensitive to crowding. It likes fair to good soil and moderate drainage. I have not tried it in clay, but it has a solid tap root so it might work. It can tolerate full sun to partial shade, and is wind tolerant.
Animals can eat it fresh or dried.
An alfalfa grower I used to work for said that a lot of the "alfalfa" pellets you buy in a bag can be as much as 45% lambsquarter. I find lambsquarter hay to be better for the goats than alfalfa. It has good protein and calcium levels without triggering milk fever. I personally have not tried it on a dairy cow, but it might be worth trying for those cows that are prone to it.