I "grew" some cheap birdseed until it was about 4 inches tall, and my silkies LOVE it. Don't blame them, it made such a soft, lush grass I'd cover my lawn with it if I didn't know it would grow 4ft tall.
Just sprinkle the cheapest birdseed blend (white&red millet, sunflower seeds) over dirt, lay a piece of burlap over it so birds won't eat it before it grows, then water liberally for a few days until it sprouts, then just every so often until it reaches a few inches. Took about a week - I forgot about it and left the burlap on it, but it didn't suffer and still came out green. Got the idea after I made the mistake of setting my trays of wheatgrass outside to get some sun, only to have the chicks decimate them.