I think I am the one who was talking about the wood frames with hardware cloth on top. They work great. But they are only for my hens to have a fresh snack. I pick the frame up and move it and them reseed it. In a day or 2 the other area is torn up. If you leave it to long they manage to pull up a lot of the plants by the root any way. Our soil is very sandy, so maybe they wont pull up the tender plants in a more clay based soil. The only thing I am changing is that I am making more of them. Mine is made with scrap 2x4s and is about 24 inches by 18 inches. I have only 6 hens in a very large fenced area.
I buy what ever seeds I feel like and also use grass seed and bird seed. I lay the frame down, pick it back up, then add some compost to the outline. Put the frame back down and sprinkle some seeds through the top wire area. I add maybe to much seeds? But they grow good, and I want it crowded. Since I have lots and lots of seed as soon as its about 1 or 2 inches tall I move the frame and start over. The hens sit on the frame and must poo into it also, but that doesn't seem to hinder it at all. We have a yard watering system that sprays in the chicken yard too, so I don't bother to water the seeds, except if I dump the water bowls I will dump them in there.